You can test drive by downloading any major bookseller's app and loading free books, for starters. That will get you comfortable, then you can branch out. I'm a heavy reader and find the Kindle app the most reliable and least problematic.
Steps:
-- Download book app, Kindle or otherwise, onto your iPad.
-- Go to bookseller, like Amazon's Kindle store, Barnes & Noble's ebook store, etc., by using your web browser (Safari or otherwise).
-- Create account with the bookseller (or use existing account).
-- Buy book(s). There are lots of free ones from public domain or freebies from publishers and writers looking to promote their works.
-- For first-time use, log on to your ebook app on iPad with the same account info as you did on the ebook seller's website. Then you should be able to load your books onto your iPad and start reading.
There are various other ways to buy and load books, but I suggest this if you're just learning, because it's easy and the booksellers have similar methods.
You also can borrow ebooks from library systems, etc.