You can add multiple desktops to the Mac OS X Mountain Lion by using Mission Control, formerly known as Spaces. Can be really useful if you are a busy multi-tasker.
If you are more of a visual person and would like to organize your folders and files using different colors, than check it out how to use color labels in Mac OS X.
You created your own movie in iMovie but you can't figure it out how to save the darn thing into a playable .mp4 file on your hard drive. I've been there, let me show you how to do that.