Unblocking someone on Facebook can be very simple. If you have blocked them in the first place then you probably already now a little bit about navigating Facebook. To unblock a person scroll to the bottom of the Facebook menu and find account settings. Under account settings will be a tab that says 'bloking' find the person's name and hit the unblock option beside their name.
This will allow that person to see your posts and explore your proflile and you can do the same with theirs. If you want to also be friends with that person you will have to send them a friend request as well.