To use My Library you must have a Google Account which is free and just requires your email address and a password. Your Google Account can be used in conjunction with many different Google services including Blogger.
I should begin by saying that if you are not already using Google Books for your genealogy, stop what you are doing and go there now! Search on your ancestor's surname, locality, religion, etc.
The My Library feature allows you to take books that you have found on Google Books and save them on a page where you can peruse them whenever you want.
Once you find a Google Book you are interested in, you can click on it and then save it to "My Library." My Library is organized according to Bookshelves. Google has labeled some of the bookshelves as you can see on the left hand side of this screenshot.
Google's labels include Favorites, Reading Now, To Read, Have Read and Reviewed. Now if these labels don't work for you, you can create your own labels. In this example, I created one called Missouri, so that I can place all the books I need for my Missouri research on one bookshelf. This is a great way to organize the books you need for each genealogy project. Use a bookshelf for each family line or locality. You can save any book on Google Books to My Library, even those which no preview or only a snippet view.
To read Google's FAQ for My Library see, http://books.google.com/support/bin/answer.py?answer=75375&topic=9259&hl=en