When you block someone they will no longer be able to do things such as tag you or see things you post on your timeline. If you’re friends, blocking will also unfriend them.
To block someone:
  1. Click ? at the top right of any Facebook page.
  2. Click Privacy Shortcuts
  3. Click How do I stop someone from bothering me?
  4. Enter the name of the person you want to block and click Block
  5. Select the specific person you want to block from the list that appears and click Block again
People will not be notified when you block them.
If you can’t find someone using this method, try going to the person’s profile and selecting Block from the menu on their cover photo.