Creating Extensions for SketchUp uses the Ruby API. Whether you’re creating plugins, extensions or add-ons (synonyms for the same thing) then you’ll need to know some Ruby. Post here if you’re creating an Extension and have any questions.
To post ruby code, prefix the code with a line with 3 backquotes.:
AFTER all of your code add another line with 3 backquotes.
The Backquote character is a key normally on the upper left of the keyboard under the ~.