There isn't much to set up to be able to connect using remote desktop. Windows server will allow two concurrent connections by default for administrative purposes. To support more than 2 you need a properly licensed terminal server.
The login required is a local account on that machine itself or an account of a domain that the machine belongs to. The login just need to have login rights on that machine. An account that is a member of the machine's administrator group can log in by default. Otherwise the account needs to have (or be in a group that has) the "Log on remotely" permission.
If you want to access a machine via remote desktop that is behind a firewall, you just need to open up the RDP port to your machine.