Stevo,
You should make a simple plugin, 1st. For example, try having an message box pop up with the text "Hello". That's like 1 line of core code, but the rest will be a wrapper that creates the actual plugin. Check out these videos: http://www.youtube.com/user/ChrisFullmer#g/u Then you can try writing your plugin. Brake it up into pieces and get each piece working, before moving on to the next. For example, 1st piece might be to simply to rotate the selected group/comp 90 deg. For user input, you can probably just use an input box: http://code.google.com/apis/sketchup/docs/ourdoc/ui.html#inputbox
You see that I went to the Sketchup Ruby API documentation, when I wanted to research how to do something: http://code.google.com/apis/sketchup/docs/index.html
-Kwok