Where do I start?

I want to make a Garry’s Mod addon but i don’t know where to start.

Use the Wiki to look up lua functions: http://bananatree.im/wiki/wiki.garrysmod.com/index4875.html?title=Main_Page

Here is a semi-helpful guide on how to create an addon in the right format: http://bananatree.im/wiki/wiki.garrysmod.com/indexa979.html?title=Add-On_Creation_%26_Folder_Structure

and

http://bananatree.im/wiki/wiki.garrysmod.com/index976e.html?title=Creating_an_addon