When you block in beach volleyball, you're close to the net and you press your hands over the net. You do this for two purposes. One, to either block the ball onto your opponent's side of the net, or two, to redirect the ball to your partner who's digging behind you.
There's two basic blocks, line and angle. A line block means that you're blocking the line straight behind you, and the angle block means that your blocking the angle side of the court. Your defender fills in the space that you're not blocking.
When you're up at the net, you let your partner know which way you're gonna block. A "one" means you're blocking line, and a "two" means you're blocking angle. You show this to your partner so that they know where to stand when they're playing defense.