To create maps/levels you'll first need to download either JED or JKEdit (I'd recommend JED because its capabilities are superior and it's easier to find documentation). You'll then want to read the Basics. After you've read those, you'll want to continue on with the Tutorials. By this time you should have a well-rounded view of editing. If you run into any problems you'll want to ask for help on the Main Editing Forum. If you run into problems with COG script, you'll want to seek help on the Cog Forum. If you just want to showcase a project or view projects from other editors, you'll want to visit the Showcase Forum. May the Force be with you.