By applications bar I presume you're talking about the menu bar at the top of the screen? That's where you choose settings for the program you're running. It won't disappear unless you're running a full screen program. Check this link out: http://support.apple.com/kb/ht2473
Nope I meant the bar at the bottom, or is it called your desktop or something? Anyway don't worry, I've found out how to do it. I love this computer so much I can't put it into words. Coming from a terrible Windows that took about a minute to boot up Chrome this is hilariously fast. It took me 5 minutes to install all of iWork. Even stuff like hooking up a printer was so easy. Simply amazing, can't believe I was considering buying another Windows.