With UNIX, there is no need to be in front of a computer to start a session with it. One only needs to connect to the computer using a UNIX connection command.
Historically, there exists two connection commands:
They take as arguments the computer name and the login name.
rlogin machine.subdomain.dom -l user telnet machine.subdomain.dom
Then, the password is asked.
Unfortunately, these commands are by design not very much secure (=the password is transmitted through the network without encryption)
It is therefore very much advised to use a secure connection command:
ssh (secure shell).
ssh, commands can be directly executed on a remote host:
ssh email@example.com [command]
ssh will connect to the remote computer and start a new interactive shell.