In the Facebook settings, you can add persons to your circles (and kick them out) The circles have different importance, like family, friends, and others you know. You can setup your account, so only family can see everything and friends can see a little less and others even less. What you allow to see depends on the settings in your account. But it is not possible they can see what is on your computer, unless you did add that to Facebook.
Better not add all your pictures to Facebook. keep the private ones in folders outside Facebook. Don't grand access to all your pictures on any of the devices.
You almost can get a degree in setting up Facebook, but the safest way to start (sorry it looks you already are on Facebook some time) is to keep everything outside Facebook. Don't grand it access to folders on your devices. Just type the things you want others to hare with you and only put pictures in Facebook you want to show. Slowly accept other people. And when you don't want someone to your circles just remove the person from your settings.
Facebook has great support and you can find everything on their help page. Study one thing at a time and make sure you understand the part you want to use. That includes, how to remove things and persons from your timeline.
help from Facebook is here:
Facebook Help Center Facebook