If you’re like most people, your Facebook timeline is constantly bustling with activity. Your friends may post things to it, your apps may post to it, and of course you are constantly posting a stream of funny cat-related memes.
You set your privacy settings up, probably long ago. At that time, you may have set things to friends only, friends of friends, or possibly even public. Chances are, you made that setting a long time ago and have never looked back since to see what audience you are allowing to view your posts.
 

 
The first time you see a notification that a complete stranger (or Facebook stalker) has just liked something on your timeline, you’ll realize that your privacy settings are obviously allowing your “stuff” to be shared with a much wider audience than you are comfortable with.
The next question you’ll ask yourself will likely be “What can the public see on my timeline?”
Thankfully, Facebook has created a feature to allow you to view your timeline as if you were a member of the general public. You can also use this same feature to view your timeline as if you were a specific friend, so you can see what they would see if they visited your page, This can be helpful in testing your privacy settings.

Here’s How to Test Your Privacy Settings to See What Others Can Access on Your Timeline by Using Facebook’s View As Tool:

1. From your Facebook Timeline / Profile, click the “…” icon.
2. Click on the “View As” link in the dropdown menu that appears.
3. This will allow you to see what your profile looks like as a member of the general public. If you want to see what a specific person would see (such as one of your friends or a non-friend Facebook user, select “View as Specific Person” and enter their name.
After you’ve found out what the public can see, you may decide that you want to restrict the public from viewing a majority of the content on your timeline.
 
Fortunately, Facebook realizes that users have A LOT of historical content that dates back for many years and that most people don’t want to go back through their entire history changing each item from “Public” to “Friends Only”. To address this issue, Facebook has created a function that will take all of your old content and change it to “Friends Only” or to whatever other audience you deem appropriate.  Facebook calls this feature “Limit Availability to Past Posts”.

To Use The 'Limit Availability to Past Posts' Tool:

1. From your Facebook profile page,  click the blue triangle icon in the top-right corner of Facebook.
2. Choose “Privacy” from the dropdown menu that appears.
3. In the “Who Can See My Stuff” menu section, select “Limit the audience for past posts I’ve shared with friends of friends or Public”,
4. Click the “Limit Past Posts” link and choose a new audience (typically you would choose “friends only” or something more restrictive).

Important Note:

Once you make this change, there is no easy undo. In order to change pasts posts after you’ve made the mass change, you would have to run this process again and choose a new audience for all posts, or you would need to manually go into each post that you want changed and modify the privacy settings for that specific post.