`hostname` - show or set the system host name

hostname [-I] [-f]

Options you will use

-I, --all-ip-addresses: Print all configured IPv4/IPv6 addresses, space separated.
-f, --fqdn: Print the fully qualified domain name.

Gotchas

Setting the hostname permanently is hostnamectl set-hostname, not hostname foo (which is lost at reboot).

Taught in

Try hostname in a real terminal Free, in your browser - a real Ubuntu terminal to try it in, with missions that check your work.