Server will = the netbios name (Server05), fully qualified domain (Server05.banditland.com) or IP address of the server (192.168.1.2 or whatever your external ip address of the router). These are just examples. Domain is generally something you would find in a corporate environment and not at home so you can leave it blank. Please make sure al accounts
Connecting on your internal network should require nothing more than the server name or ip. If you are trying to get to this server remotely from another location like Starbucks, then you'll need to know your external ip which you can get from whatismyipaddress.com before you leave. You'll need to know how to configure your router to forward RDC from the outside world to your inside world.
I highly recommend changing the default port from 3389 to something else or at least mapping a different external port to the inside port of 3389. Most consumer router/firewall devices can do this.
These are the basics which 99% of the remote apps require you to do whether it be RDC or VNC. Generally only the ports change.