I erased some unnecessary fonts and now my MacBook won't display any words/icons? Apps aren't working as well. Help!

Well, that depends on which OS you are running; in any case you will need to reinstall your OS since the fonts are part of the system.

So, if you have an install disk, boot from it, and reinstall your OS. If you have Lion or newer, use recovery (Command + R during startup or restart) and choose to reinstall the OS.

OS X has several different versions; in order to answer that, you need to post a) which version your Mac shipped with and b) which version you are running now.