Online
A ranked duel against a live opponent. Matchmaking looks for someone close in strength; if nobody is around it offers a bot battle and says so openly.
Four ways to play
The same battle, different opponents and different stakes.
Friends
Invite someone by callsign and play against each other. A rematch starts with one button, right from the results screen.
Bots
Practice without rating: the same ships, the same weapons, a program for an opponent. Good for trying a new class without risking your place.
Training
A first battle with a hint at every step: placement, ship selection, aim, shot. Takes a couple of minutes and pays coins for your first ship.