Summarize this article in one sentence.
It's a blue app with a white f. If you're not signed in automatically, log in. As you type, a list of Facebook profiles will appear below the search field. Doing so opens their Facebook profile. It's on the right side of the screen, below the person's profile picture. The person you block will automatically be unfriended and will not be able to contact you via Facebook or Messenger.

Summary:
Open the Facebook app. Tap the "Search" field at the top of the screen. Type a friend's name in the field. Tap the name of the friend you want to block. Tap or More. Tap Block. Tap Block to confirm.