One card each against the dealer, highest wins.
The simplest game in a casino, and the children's game War with a house edge attached.
You bet, then you and the dealer each receive one card. Aces are high. The higher card wins even money, and the lower loses the bet. Suits are ignored.
Everything interesting happens here. On equal ranks you choose:
Surrender and lose half your bet. Go to war: place a second bet equal to the first. The dealer burns three cards and deals one more to each of you. If you win, you are paid on the second bet only and the first is returned — so you risk two units to win one. If you lose, both are gone.
Some tables pay a bonus if the second round ties again.
Going to war is the better of the two choices despite the odd payout, and surrendering is the worse one. There is nothing else to decide.