When you invoke this command from the DRAW menu, it prompts you to click on a field, and then draws a 5 pixel thick rectangular border around that field, spaced out 2 pixels from the field's outer edges.
This produces an especially nice visual effect with Rectangle fields, i.e. fields whose style is "rectangle" and which therefore already have a thin visible border. Such fields look good in organization charts, for example.
When you use the command button instead of the menu, no prompt will be given.