When a player passes the puck to a teammate then continues skating forward and his teammate passes the puck back to him almost immediately after receiving it. A give and go is a tactic used by two players while attacking the other team, and it is used often when starting an offensive rush and in two on one situations in the attacking zone.
What makes a give and go effective is that is consists of quick passes between two players, making it harder for opponents to defend because the puck is moving quickly between different players. In a two on one situation, the lone defender will usually try to prevent passes between the two attacking players, but if they manage to complete a give and go successfully, one of the attackers will usually be wide open and have a clear path to the goaltender because the defender may be caught off guard by the multiple passes between the players.
A give and go only involves two players on the same team; if a third player is passed the puck, then the situation is not a give and go. If a player receiving the puck decides to carry it for some time before passing it back to the original puck carrier, then that is also not a give and go situation.