Welcome to MobileRead Gail.
I have a 505 which I absolutely love and I have found many free books to put on it. Check out the free ebooks here at MobileRead (click on the 'ebooks' button in the blue bar at the top of the page).
You can share some books, but not all. The situation is rather complicated. Check out this thread for more information --
https://www.mobileread.com/forums/showthread.php?t=46262