To find out what stairs you can currently challenge someone in, first go to the Main Stairs Page, then click on "Show your stairs only" link. The ones in BOLD are ones you can make a challenge in. .
BerniceC: The idea about ratings is that they are a gauge of ability. (Not strictly true but we won't go into that). A high rated player is deemed stronger than a lower rated one. The thinking then is that if a weaker player draws with the stronger player then they must have played better. (Pretty much true in Chess, not so true in Backgammon). But that means they played better when the rating says they should have played worse, so the ratings need to be adjusted to fit reality. Thus the lower rating goes up a bit and the higher one comes down.
(ocultar) Si deseas jugar una partida contra un adversario de nivel similar, puedes definir en tu invitación de nueva partida un rango BKR apropiado a tu interés. En tal caso, nadie con un BKR fuera de dicho rango podrá ver o aceptar la invitación. (Katechka) (mostrar todos los consejos)