I've signed up for a GoodReads account, but I'm extremely confused about exactly what I'm supposed to do - do I log all the books I've ever read? (I could never remember!), or do I log all the books I read from my registration date onwards? How do some people thousands of books logged without remembering everything they've ever read?! Nobody can do that. What do I do if a book I'm reading isn't listed in their catalogue? Will I be kicked off if I don't read "fast enough"? Is it a reading website or a popularity contest?

It's definitely the strangest website I've ever signed up for. Are there any alternatives? What exactly IS its purpose?