In order to learn the sport of rugby you must first understand the reason it is played. In order to do this you must first play the sport of rugby. This is easier said than done.
Rugby is a game of flow, both offense and defense is required of every good rugby player. Rugby is played on a pitch (field) 100 meters long and no more than 67 meters wide with goal posts at either end.
The game is eighty minutes long with each half being a length of forty minutes a piece. A try (goal; touchdown) is scored when a player of one team places the ball down within their opponents try zone (end zone). Each try is worth five points with a kick after (extra point) worth two. Three points may also be scored when kicking the ball through the opponents goal posts without scoring a try (field goal).
In rugby play rarely stops except for the occasional blood susbstitution or pansy who asks for another minute to get his head straight or tie his shoe. The sir, or refree's watch may then be stopped at his discresion to conserve time of play.
The game of rugby is of course much more complex, and requires ample amount of explaining as well as showing. So if you would like to learn a little bit more about the game, here are some videos to help you with some of the concepts.