The good news is that most apps behave in a similar fashion; thanks to Apple's interface guidelines. You'll quickly learn what icons tend to hide what features, and what gestures to try.
Somewhere around there there are links to the Apple iPad User Guide. Hmm, there they are:
Going through it will familiarize you with the conventions you will find in most apps, and other useful tidbits.
Apple does supply these links/info in the box. They could make it a little more obvious though. It's all on the back of a rather small card in rather small print. It has a picture of the iPad and what the buttons do on the other side.