If you have played Tetrinet you should have a big head start. I assume you know how to play regular Tetris.
This game is Tetris with weapons.  For each line you clear, a block with a letter on it will appear in your field.
These lettered blocks are weapons and can be used on your opponents or on yourself (some of them are good).
When you clear a line that has a weapon in it, that weapon will go into your inventory.
To use the current weapon on an opponent (or yourself) you press the button that appears above their field (A, B, X, Y).
You can change which weapon is current by using the right thumbstick.
The game decides how many people are playing based on how many controllers are plugged into the xbox.

Here is a list of the controls:

DPad Right/Left/Down     Moves the shape right, left, and down
DPad Up                  Drops the shape all the way to the bottom
A, B, X, Y               Use the current weapon on a player
START                    Mark yourself as ready
BACK                     Mark yourself as not ready, during a game it discards the current weapon
Right Thumbstick         Change which weapon is current (blue highlight)

Here is a list of all of the weapons and what they do:

A     ADD LINE       Adds a line 
C     CLEAR LINE     Clears a line 
UP    FAST           Speeds the up falling block 
DOWN  SLOW           Slows down the falling block 
N     NUKE           Clears entire field 
B     CLEAR WEAPONS  Clears all weapons from field 
F     FLIP           Flips field upside down 
S     SWITCH         Switch fields with another player 
R     RANDOM CLEAR   Clears up to 10 random blocks from field 
G     GRAVITY        Sucks all blocks down to the bottom filling in all holes 
Q     QUAKE          Randomly Shifts each line to the left, right, or center 
O     BOMB           Ignites any bombs currently in the field causing the surrounding blocks to blow up into the field  

A quick start tip, yellow weapons are bad and should be used on opponents while purple weapons are good and should be used on yourself.
Flip and Switch are green since they could be good or bad. 

Join us in #bbx on efnet and let us know what you think.