Technically what we're playing is called Futsal by FIFA.  However, the Futsal rulebook is almost 100 pages, so we try to condense things to make the important points simple.

The field is 20 by 40 yards.  Instead of a penalty area, you have a penalty arc.  The dimensions of the Futsal field correspond to an international basketball court, since that is the surface on which the game originated.

The game is played in two 20 minute halves with a 5 minute halftime.  Subs are done on the fly.  You have 4 field players and a goalkeeper.

There are no throw ins.  The ball is placed in play via an indirect free kick from point on the touchline where it left the field.  There are no goal kicks.  The goalkeeper puts the ball back into play by a throw from inside the penalty arc.  The rule differences document on the sidebar lists conditions in which the keeper can handle the ball.

Shoulder charging is not permitted.  It is an indirect free kick.  Slide tackling is also not allowed.