When the trigger man calls out "CIRCLE"  the corner man knows to run quickly and "circle around"  to the opposite side corner.

In this example, 3 is the trigger man.  Upon calling out "CIRCLE", 1 runs to the opposite corner leaving 3 and 4 alone on the left side.

("Circle" can also be called out by the point guard.  In this case if the point guard calls "CIRCLE" and he then passes to the wing, he will then cut through to the basket and continue out to the opposite corner area.  If the point guard instead dribbles to the wing then the wing man clears out to the opposite corner area.)

This results in a 2 on 2 game.  

4 then sets a screen on the baseline side of 3's defender, then rolls to the basket after setting the screen.  3 dribbles off the screen from 4 and can either look for his shot or pass to 4 rolling to the basket.  

1 and 5 look to CRASH the boards if a shot is taken.
2 stays at the point for defensive protection.