In practice, this node is ideal to use when you're trying to take an attribute from one thing and transfer it to another based on position.  Point and primitive numbers do not need to match up for this node to work.  They just need to be close to each other for the attribute to hop from one geometry to the other.

Source/Destination Group + Types:

--  These parameters are asking you to select certain points/prims/vertices to be considered when this node goes to operate.  For more info about groups, please visit the Group Node Bible entry.

Attributes:

--  The attribute parameters are asking you to specify which attributes you'd like to transfer.  You can use the dropdown menu to select attributes, and if you'd like multiple attributes, you can separate them with spaces.  (For example: attribute1 attribute2). 

--  If this field is left blank, then it will take all attributes and transfer them.  Use the "^" syntax to say "except" and the "*" syntax to say, "all" and "*term*" to term-search for something. 

--  So as an example, "I want everything except for the mass attribute" = * ^mass
--  Or as another example, "I want every attribute with the term "piece" in the attribute name" = *piece*

Copy Local Variables:

--  In Houdini, there are certain expressions that utilize the $ sign.  As an example, you can say, "$F" to return the frame.  Well, certain nodes have special variables that are understood by that node, and this parameter allows you to transfer over those variables as well as attributes when this goes to operate.  In practice, I would suggest ignoring this parameter because it's not used very often in modern workflows.

Allow P Attribute:

--  By default, the attribute transfer will not change the position of your points by affecting the P attribute.  You can change that though with this parameter.  Specify P as one of the point attributes you'd like to transfer and turn this on to override the default behavior.  In practice, this can create some cool looking abstract FX.

Kernel Function + Radius:

--  The various Kernel Functions are used to determine how multiple sampled values are blended together.  In order to see this work, you need to turn up the Max Sample Count to a value greater than 1.  In practice, I also like to turn the Distance Threshold off and raise the Blend Width parameter until the point attributes start hitting the destination mesh.

--  To see this in action, watch this Gif:

Max Sample Count:

--  This is asking you, "how many values would you like to blend together when they overlap?"

Distance Threshold:

--  The Distance Threshold seems to snap values without feathering.  

Blend Width:

--  This parameter gets added on top of the distance threshold and seems capable of feathering.

Uniform Bias:

--  This mode is only available when the Kernel Function is set to "Uniform Model."  In this situation, it will control the feathering of values by doing a linear interpolation between the source and destination values.  Here's what it looks like: