An americano is a club night where you get a new partner every round. You are not in a team and there is nothing to be knocked out of. You play with somebody different each time, against two more, and the night keeps a running total for you.
What you score
The points your side won. Not the match, the points.
So a round played to 24 that ends 15-9 gives you 15. Losing it costs you nothing else. A good round with a partner who is having a bad night is still a good round for you.
Highest total when the last round is in wins the evening.
Who you play with
Whoever you have not played with yet. The night deals the partnership nobody has had, every round. So you work through the room over an evening, instead of landing beside the same person twice and never meeting somebody else at all. If your club plays long enough for everybody to have partnered everybody, it starts again.
You do not have to arrive at the start. Turn up at round three and you are put straight on a court, because you have partnered nobody yet.
Sitting a round out
Four people fill a court, so if the numbers do not divide, somebody sits. It is spread across the evening rather than falling on the same two people, and sitting out costs you nothing except the points you were not there to win.