It doesn't compile and I don't know why

First up: The arduino program has a small region at the bottom where it shows error messages in red text. Unfortunately it usually scrolls past the first error message and only shows you the last part, which is not very helpful. Make the error region larger and scroll up to find the first error message.

If that doesn't help, go here: http://therebelarmory.com/thread/10207/proffieboard-newbie-thread and post your config file and complete error message, and someone will help you figure out what the problem is.