Oh you'll have fun! I love Rally (and luckily, so does Quigley

)! The best thing about it is that there is no limitation on verbally communicating with your dog, hand signals, patting your leg, etc., so in that regard it's easier than traditional obedience.
Don't worry about being confused about the course, you'll get used to it fairly quickly once you've had a chance to work on it in practice in a Rally class. And at a trial you have some time to walk the course (without the dog) before judging begins, so you don't go out unprepared.
Of course that still doesn't preclude making mistakes at trials (I'm the best example for that

), but it's all in good fun.
You can look at descriptions for each exercise sign here:
http://www.akc.org/pdfs/about/board_minutes/Rally_Regulations.pdf(Starting on page 10 of the "Rally" part)