Far too big and valuable to wear on your arm, LurkingandLearning.
You access the internet on it via wifi unless you have a more expensive 3G model which means you can use wifi and also pay to access 3G via Vodafone, O2 or similar. So if you are in a class you will only be able to go online if you have wifi access or are paying for 3G data.
You can go anywhere you like online using Safari (like firefox or Chrome), or use apps.
I would recommend Notability for taking notes. You can create categories for your notes (could be used for different classes) and then have a bunch of different notes under that category. I think it's relatively inexpensive.
You can buy books via whatever Apple's own system is, or from Amazon for the Kindle app. There are some free books, and many many cheap ones. If you want a regular bestseller it will probably be closer to normal price (as it should be, imo, if we want good book publishing to survive - tangent!).
You might have a bit of a learning curve when you first get it, but basically you can use it to play music, go on internet, use as a productivity tool, play games, keep photos, etc. I love mine :)