You know tetris. The blocks fall and stack on top of each other. Rotate and shift them before they set to try to complete rows. When a row is completed, the blocks therein clear, and all higher rows shift down accordingly. I maybe could have explained that better, but if you don't know the rules of basic (single-player) tetris, this isn't the game to start with.
Now for you tetris enthusiasts out there, here are some metagame details:
Now, here are the controls:
Those are the controls. In theory. Every piece, the three 'basic' controls (left, right, rotate) are assigned randomly to members of your team. You have to work TOGETHER to manipulate the piece the way you want.
Multiple players might have the same available controls. Certain players may have no available controls, or all three, etc. The only guarantee is that each control will be available to at least one person on the team.
If you try to use a control that you don't have, the piece auto-drops.
Let's kick it up a notch.
There are three game modes you can pick.
Anyway, that's how everything should work. Tetris Buddies is still very much in beta, so if you find some bus, let me know in the feedback section.