Main Parameters:

Source Group:

--  As mentioned above, you'll want to use this field to specify which field you'd like to preview.  Use the dropdown arrow to select which volume you'd like to read.

Method:

--  The volume visualization node gives you the option to preview values using a mesh, volume, or points.  In most situations, I would recommend using mesh, but if your volume is hi-resolution, then you might want to switch that to points for better performance.  If you choose volume, then a 2d volume will be created and populated with the corresponding voxel values.  For more information about 2D volumes, please visit the volume node bible entry.

Plane:

--  Determines how the plane will be oriented along the volume.

Offset:

--  This will adjust the location of the plane along the volume.  

Attribute:

--  This is NOT the name of the field that you are trying to access data from.  If you are using Mesh or Points, this relates to the attribute name that you see in the geo spreadsheet.  The nearest sampled voxel values will then store under this attribute name.

Local Variable:

--  This allows you to make a local variable which contains the voxel values.  In practice, I would general advise against
using local variables.  It's usually better to just use attributes for storing the sampled values.  The option is here, however, and according to the docs, "A local variable will be made mapping from this to the attribute.  If left blank, the attribute in ALL CAPS will be the local variable."

Visualize:

--  Colors the points/prims according to the sampled values.  

Visualization Ramp:

--  Gives you options for how you would like the points/prims to be colored.

Visualization Range:

--  Represents a range of values that get used for determining how things are colored.

Keep Original Geometry:

--  This keeps the original volume after the volume slice operation has occured.