To block someone:

1. Click the account menu at the top right of any Facebook page and choose Privacy Settings.
2. Find the Block Lists section and click Manage Block Lists.
3. Enter the name or email address of the person you want to block and click Block. 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 (timeline) and selecting Report/Block This Person from the dropdown.

If you still can’t block someone using the methods described above, it’s possible that this person left Facebook or restricted their privacy settings. You can still prevent them from viewing your profile (timeline) by adjusting your privacy settings.