Yes, you certainly can. When you find a book in the online catalog that is checked out to someone else, you may "place a hold" on that book -- that is, ask the Library to hold the book for you at the Circulation Desk when it is returned so that you will be the next person to get it. From the Brief or Full Record screen for the book you are interested in, click on the hold link under actions in the filter box, then follow directions to place the book on hold.