The Flow of the Game
A hockey period starts with a face-off in the center of the ice. During a face-off, one player from each team, usually a center, will line up at one of the designated face-off spots opposite one another. All the other players will line up defensively behind their teammate who is conducting the face-off.
An official will drop the puck between the two players' sticks and each will try to get possession of the puck or pass it to one of their teammates. Then the teams are off!
The team in possession of the puck is on offense and is trying to score points by getting the puck into the opposing team's goal. The other team is on defense trying to stop them from advancing by stealing the puck for themselves and blocking shots.
The team on defense can check players on offense to try to stop their progress. There are many different types of checks, but the most popular types are stick checking, body checking, shoulder-checking, and hip-checking. In each of these checks, the defensive player will drive his body into an offensive player (usually against the ice hockey rink side boards) to prevent him from making progress. As you can imagine, checks can lead to serious injuries, so there are a bunch of rules about which are legal and which are penalties. In general, any checking from behind, where the player on offense can't defend himself is a penalty.
There are three major rules that restrict movement of the puck. The first, is that the player cannot go offsides. This is a bit different from the offsides rule in football or soccer. In hockey, a player is offsides if he enters his opponent's territory (as seen in the image to the left) ahead of the puck, meaning he must be handling the puck in front of him before he crosses his opponent's blue line.
The second rule prohibits icing the puck. This means that a player cannot shoot the puck from behind the red center line past the opposing team's goal line without being touched by another player. It is not icing, however, if the puck makes it into the goal or the goalie must push it away to prevent it from being a goal. Icing the puck is also allowed if the team is short one or more players because of penalties.
The third rule is that the puck must remain in play. The puck goes out of play when it is pushed into either team's bench area or it goes above the glass surrounding the rink.
Otherwise, hockey is super straight-forward. Play is only stopped at the end of each period or when officials blow their whistles, i.e., when the puck goes out of bounds or penalties are called. Play resumes within each period with a face off at the nearest face-off spot.