When using chops, it's often useful to bring in the transformation of an object into CHOPS so that you can alter it.  The Get World Space will do just this.

-  "The left menu chooses the order in which transforms are applied. For example: scale, then rotate, then move. This can change the position and orientation of the object, in the same way that going a block and turning east takes you to a different place than turning east and then going a block.

The right menu chooses the order in which to rotate around the X, Y, and Z axes. Certain orders can make character joint transforms easier to use, depending on the character."

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Channel

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The Channel tab determines how this node gathers parameter information.  The parameter values get stored in a "channel" which you can see if you middle-mouse the node.  Keep in mind that in most situations, the defaults ought to be fine.  If you do change your framerate to 30, however, then be sure to change the sample rate to 30 as well.

In other words, channels come from the parameter(s) that you're gathering information from.  Channels sample those parameter values.  How the channel samples the parameter is determined by the settings in the channel tab.

The user documentation is quite poor in this section, and it is difficult to find good information about some of these parameters elsewhere.  With that said, it's important to understand a few key features about CHOPS:

Rather than evaluating at a single point in time, CHOPs deal with the timeline as a whole and store all evaluations at once in memory.  That's kind of like reading a whole chunk of values all at once instead of one at a time.

Also know that channels can start and end on specific frames.  It's possible to say something like: "On frames 1-20 override parameter "x," but at frame 20, stop the channel override by getting rid of the channel in CHOPs.

To make things more confusing, different channels can start/end at different times.

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Align:

--  The best way to wrap your head around this parameter is to imagine all the sampled values existing as a block of information that exists within a frame range.  How these blocks are "Aligned" along the range of specified frames is what this parameter is trying to determine.  See the image below:

 

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If this mode is enabled, then you can sculpt onto the mesh.  These settings control the behavior of the sculpting brush.  To activate this in the viewport, hover over the viewport and press enter.  If this does not work, then create a brand new edit sop and try again.  -- Caution --  If you have any serious sculpting work that needs to get done, then do it in Zbrush or Blender.  The Edit SOP is not designed for capturing a good sculpting workflow and can be very buggy.  It's only useful if you want to do a few basic touchups on something.
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This section controls how the brush should behave.  NOTE - If you change settings in the parameter window, those settings will not apply to future strokes that you do in the viewport.  It's always better to right mouse in the viewport and select what you want there.

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Goal:

--  Deform Points = Points will move in or out.
--  Smooth =  Averages point positions
--  Deform & Smooth = Does as it says
--  Erase Changes =  Reverts an area back to the state something was before edit sop made any changes.

Axis:

--  Normal = When deforming points, it will move the points in the normal's direction
--  X,Y, or Z =  When deforming points, the Edit sop will move point in this direction.
--  User Defined/Vector Field =  When deforming points, the Edit SOP will move points in the direction specified in the "Vector" field.

Accumulate to Stencil & Apply and Clear Stencil:

--  According to the docs, "By default, the operation is applied and the stencil cleared after every brush stroke. With this set, the stencil is not cleared until "Apply and Clear Stencil" is pressed." 
    Here's another way of saying that... the accumulate to stencil makes it so that brush stroke isn't complete until you press the "Apply and Clear Stencil."  Normally your brush stroke is done when you let go of the mouse.  This is like keeping the mouse held down until you press the button.

Update Displacement Normals:

--  This will re-compute the sculpting normals used by the sculpting operation.  NOTE this is not the same thing as using a normal SOP after the edit.  The edit node will not update your viewport normals after each stroke unfortunately.  For this reason, I would recommend setting a normal node after the edit sop to see updated viewport normals.

Apply to All:

--  Applies the sculpting operation to all points.  This may be especially useful when you want to smooth everything.

LMB Displacement:

--  How far to deform points when using left-mouse

MMB Displacement:

--  How far to deform points when using middle-mouse.  In practice, I can't get this to work.


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Brush:

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The brush section deals with the brush settings in the viewport.  Unlike the Operation Tab, any changes you make in this tab will reflect in the viewport properly.

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Shape/Bitmap:

--  Defines the brush shape.  The bitmap option will become available below if you decide to use a stencil for your brush shape.

--  This tells Houdini which color channel it should look at when using a texture map for the brush shape.  By default it's "Alpha" but I would recommend Luminance as a better default.  Many images don't have an alpha channel, so just be sure to clearly specify which color channel is going to be used for the black/white values.

-- This defines how large your brush is.

UV Radius:

--  If you were to use a brush in a UV viewport pane, then this would be the size of the brush in uv space.  This doesn't make much sense for the Edit SOP however and I would generally ignore it.

-- How sensitive should the pressure be on a tablet?  A high value is less sensitive to pressure.  Lower values are more sensitive to pressure.

--  Some operations can benefit from a 3d brush.  Altering hair curves may be a scenario where depth sculpting may be useful.  Enabling depth will turn your surface brush into a 3d one.  The first field is asking you how far into the surface it's allowed to go.  The second field is asking you how far away from the surface the brush is allowed to go.

--  According to the docs, "How far to rotate the brush."  In order to understand what this actually does, you'll need to change the up vector type to "Fixed" and add some brush squash to change the shape.  Once you do that, the Brush angle will rotate the brush and you'll be able to notice a difference.

Brush Squash:

--  Changes the shape of the brush and squashes it.

Opacity:

--  When using a stencil, this will essentially alter the intensity of the brush operation.

--  If this is set to 1, then the pressure from your tablet is allowed to affect the intensity of the brush stroke.  If it's set to 0, then you'll get the full opacity right away.

Brush Splatter:

--  Adds a noise to the intensity of the brush stroke.  The position of the brush will change the noise pattern

Paper Grain:

--  This also adds a noise.  This time the noise changes based on object position.

--  This feathers the brush intensity on the inside of the brush radius.

--  This Kernel affects the falloff that's used inside the brush when it goes to falloff.

Up Vector Type:

--  This orients the brush.  The stroke direction will cause your brush to rotate based on the direction that it's moving in.  You can be more specific though by choosing "Fixed" instead.  If that's the case, then you'll need to specify an up vector telling the brush how it ought to rotate.

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Stroke:

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This section captures data that's made by the brush stroke.  In addition, it has some options for how the brush ought to be oriented along the surface of the mesh.  For the most part, you shouldn't need to worry about this section much at all.  If you modify a value in this tab, it will not affect the viewport unless it's a toggle option.

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Orient Brush To Surface:

--  This will do just as it says.  The brush will follow along the surface as you hover over it in the viewport.  There may be situations where you'll want to turn this off, however.  If you want to edit points or apply paint based on your view rather than the current shape of the surface, then you might want to turn Orient Brush To Surface off. 

Use Connectivity:

--  "If set, the tool will only affect points connected to the closest point to the intersection. This is usually a good thing, as it avoids accidentally painting through the geometry (but see the depth parameter), but can prevent smoothly painting across seams."

Use Normals:

--  There is no documentation, so the use of this option is unclear.

Realtime Node:

--  Applies changes as you brush (that is, while you are still holding the mouse button down) instead of at the end of each stroke. This is less efficient, but lets you do things like paint on surfaces while playing the animation.  I'm not sure why you would want to paint something during an animation, but alas, it is possible.  Keep in mind that the quality of the brush stroke goes way down though.

Direction, Hit Location, Hit Primitive, Hit UVW, Hit Pressure, Hit Point, and Event:

--  All these settings are here to capture data as you paint.  They are not parameters that you will adjust manually in the parameter window.  In practice, you don't need to concern yourself with this.  Have a look at the user docs if you're curious about what these do though.