This color should not be confused with adding a texture map to something.  If you're trying to do this, then it's better to add a texture map within the shader.   Additionally, if you'd like to preview a texture map within your viewport, then you'll want to use the UV Quickshade node instead of this node.  The color sop is simply there to add an attribute which exists on your mesh or detail context, and it can be also be used to preview things in the viewport.

Group:

--  This can apply the Cd attributes to specific groups, or a selection of point/primitive ids.  To add a group, use the group sop above this node.  To select specific point/prim ids, then use the arrow next to the dropdown menu button and select them in your viewport.

Group Type:

--  Be sure to select the appropriate group type if using groups.

Delete All existing Color Attributes:

--  It's possible to have different color attribute values assigned to point and primitives.  This makes it difficult for the viewport to understand which one you want to see.  So, to simplify the process, you can click "Delete all existing color attributes" to clear all instances of Cd before applying the new color specified in this node.

Class:

--  Should Cd exist as a point, primitive, vertex, or detail attribute?  For more information about attributes, please visit the attribute create sop.

Color Type:

--  Constant:

    *  Evenly applies one color to all selected points/prims.

-- Bounding Box:

    *  Draws a bounding box around the incoming object, and adds color based on it's relative x,y,z components within that box.  

--  Random:

    *  Applies a random color for each point/prim

--  Ramp from attribute:

    *  To use this parameter.... 1.  Specify an attribute that will control which color gets assigned.  2.  Specify the range of values used to determine these colors (ex: If your attribute goes up to a value of 10, then you want to say that the range goes from 1-10),  3.  Select the colors which correspond with the attribute values.  Colors to the right of the ramp correspond with the maximum range value.  Colors to the left correspond to the minimum range values.

--  Random from attribute:

    *  To use this parameter... 1.  Specify an attribute that will control which color gets assigned.  The attribute value is now used as a seed for a random color.  2.  Adjust the seed as necessary for differently assigned colors.