Everyone is ranked from the top down. You climb by challenging players above you and beating them. It never ends — the ladder is always on.

Register to play. The ladder is the only game that needs your email — it's how challenges reach you. You join at the bottom.
Who you can challenge: anyone up to 3 places above you, as long as they aren't already in a challenge.
Locked in: once a challenge is sent, both players are locked until the result is in — neither can send or receive another.
3 days to accept. The player challenged has 3 days to accept, from the link in their email or signed in on the scorer. Only the two players can accept, change the date or enter the result. If they don't, the challenge is scrubbed and counts as refused.
3 refused and you drop. Every third challenge you don't accept in time drops you one place.
Date and venue. Once accepted, one player suggests a date and venue and the other confirms it or suggests another, until it's agreed.
If the challenger wins they take the other player's place, and that player and everyone between drop one place.
If the defender wins nothing moves — they've held their place.
Each challenge is played to the ladder's format (for example 501, best of 3 legs, double out).