How can I block someone in accessing my Facebook account?

First you delete that person that you want to block . ( hopefully you know how to do that) Then once they aren't your friend go to their profile . Now your at their profile scroll down and on the left there is an icon that says block this person . And there you go. hopefully it works that way on your computer . i have a friend who said the icon didn't show up . for most people it does though.