I click on a book in the Catalog, but all I see is a list of words that are supposedly from that book. There’s also a “Set Active” button, but I have no idea what that means. I can’t find the actual book text anywhere. Am I missing something?
You can’t read the books on this site. It helps you learn new words and plan your reading, but you have to get the actual book yourself.
Hi Lexie. MaximusDeMe is right ReadOriginal is currently a tool for preparing your vocabulary before you read books. The word list you see for a book shows which words from that book are worth learning, since they are used multiple times in the book.
We can’t provide the complete book content because of copyright, so for that you would need to upload your own copy. Most Catalog books, though, have a “Read sample” link below the cover, which gives you access to the first pages of the book. This lets you start reading and see what the book is like—is it too difficult, is it engaging, etc.
… for that you would need to upload your own copy
Hmm. I uploaded an EPUB file on the Uploads page, but I still only see a list of words. So there’s no way to read even my own file? Why would I upload anything then?
When you upload your own file, you can see sentence examples on Queue page 
It helps to see real examples from your book when you learn new words.