For whatever reason you are deciding to remove the access for the public to view your profile. In order for any one who isn’t your friend on FB to see your profile, they will have to request friendship. If you do not know the person, DON’T ACCEPT THEM.
Here is how to make you profile private:
On top right hand side you will hit the little blue down arrow and find “settings”.
Once you are in the settings, you will see this & click on “privacy”
Then you will go from there.
You will then edit the first line and change it to which ever level of privacy you would like.
Hope this helps you turn your profile from public to PRIVATE.