A Facebook troll is a person who is caught trolling your profile, leaving you inappropriate posts or sending unwanted messages with the purpose of disrupting your daily life or to gain attention from you and your friends. You can put a stop to a troll quite easily on Facebook with the site's privacy settings, restricting what the person can view or post.
Sign in to your Facebook account and go to the person's profile that's trolling your page. Scroll to the bottom of the left column and click the "Report/Block This Person" link. Select one of the appropriate options for the situation, such as "This person is annoying me" or "This person is bullying or harassing me." Click the "Continue" when done.
Block the troll's profile if necessary. This will fully prevent him from seeing your profile and contacting you. Additionally, you won't be able to see his profile or contact him. To do this, click "Report/Block This Person" link, select the "Block" box on the dialog screen and click "Continue."
Edit your privacy settings to prevent what a person sees on your profile and how someone may contact you. Go to the "Account" menu at the top and select "Privacy Settings." Under the "Connecting on Facebook" section, click the "View Settings" link. From this settings page, you can control how you appear in search results, who can send you friend requests and messages, see your friend list and other contact information.
Click the "Back to Privacy" button at the top of the page and go to the "Sharing on Facebook" section. Click the "Customize Settings" link. Review the privacy settings on this page to see if there is anything that you would like to restrict, that might be helpful avoiding contact with or revealing your information to new Facebook trolls.
Approve only people you know and want to connect with on Facebook. This should go without saying, but many times a person will accept a friend request from someone unknown. If you restricted the ability for people to send you friend requests, you wouldn't need to worry about this, but it's always good practice on any social network to only accept request from actual friends or colleagues.