Go to English class, too, please.
You can't have your hard drive full. 15-25% of your drive space needs to be free. That means that you have to have some number over 20GB free. Open a finder window (click the goofy apple face on your dock), click on your home folder (the one with your user name and the house picture), and then look at the bottom of the window in the bezel. What number does the text say and what appendage? 1GB? 750MB? 86GB? If you have over 20-25GB free and you're still getting the spinning beach ball of doom, then get an external hard drive and immediately back up your data. Otherwise, get an external hard drive and start moving crap onto it, now. Also you might try restarting your computer in the meantime, and also stop having every application that you own open at the same time. You quit applications from the file menu.