Welcome to MobileRead, soozie!
You can use any number of apps to read on your Galaxy Tab. Which size did you get, by the way?
See the big list of reading apps in the sticky at the head of this forum. This means you can read many different formats, including but not limited to pdfs. Where will you be getting your books? You can use the Amazon Kindle app, or the Barnes & Noble Nook app, for instance, if you want to buy your books from either of those companies.
If you want to download library books you will be dealing with DRM and probably will want to use your Adobe account (for epub and pdf), although libraries now also carry the Kindle format.
Another important question is whether you want to keep your books on a computer (PC/Mac) as well as on your Tab. If you do you can download the books to your computer and then import them to the Tab over a wireless LAN connection or you can email them to yourself. You might want to use Calibre as your main library, if you haven't started doing that already.
In other words, you have a lot of flexibility!
Good luck, and have fun!!