Q: How to remote access network computer?

I've been looking for plenty of ways to access my network computers and monitor them. I've been looking at OS X El Capitan: Share the screen of another Mac and OS X El Capitan: Share your screen. When I do OS X El Capitan: Share your screen, the "Sharing" option does not allow me to access it due to school property. I've followed OS X El Capitan: Share the screen of another Mac. It worked up until the part I had to press "Share Screen". I try to access it with login credentials to the computer, but somehow it does not work. Anyone know the solution to this?

If I'm not being clear enough, please say so, I'll try explaining a little more about my problem. Thank you