How to do remote computing?

Hello guys,

I'd like to do some remote computing but I don't know how to connect two PC's. One- the one I'm working on- needs to log into the Server, right? If I do, it alerts 'Connection refused'. I also haven't set up anything on the Server. There is the Option 'Remote Computing' in the Preferences, but what do I have to insert there?

Could someone tell me about the Basics?

Thanks in advance,
Philipp.