`ip` - show and manipulate routing, devices and addresses

ip [-br] [-c] [OBJECT] [COMMAND]

Options you will use

a, addr: Addresses. ip -br a is the readable one-line-per-interface form.
l, link: Interfaces and their state.
r, route: The routing table; default via ... is your gateway.
-br, -brief: Brief tabular output.

Gotchas

enp0s1: en = Ethernet, p0 = PCI bus 0, s1 = slot 1. Predictable naming, so the name does not shuffle between boots the way eth0 could.

Taught in

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