brodie: you're fine with the basic/free app.
The Pro app is ad-free and adds a couple of nice-to-have extras like little graphs of lap times and the ability to do interval training.
More details here: http://www.endomondo.com/features
ahwiles: happy to point you in the right direction.
Basically all you do is run the app on your phone. Set your Sport to Cycling, Transport, check you have GPS reception then hit Start when you start your ride and Stop at the end.
It records your "Workout" using the phones GPS and automatically uploads it to the website when you finish. It will be automatically counted in any challenge you have joined too.
All your previous rides appear under the Workouts tab on the website, where you can also look at maps, statistics etc.