Each team has 15 players. Substitutions are allowed in international play, but a player who leaves the field (or "pitch") may not return to play unless he has left momentarily to attend to an injury (set a bone, stitch up a cracked head, sew on a limb, etc.) Each half is 40 minutes and there are no time outs.
The goal is to score as many points as possible by carrying, passing, and kicking an oval ball into the scoring zone or "in-goal" area. The ball can be run forward or kicked forward, but it can only be passed backwards or sideways.
Players are tackled when their forward progress is stopped. A standing player who has been stopped is considered tackled. Only players with the ball can be tackled. Players must tackle with their arms and not shoulders and must hit the ball carrier below the shoulders. Players cannot intentionally throw a ball "in touch" (out of play) to stop play. They can, however, kick the ball into touch.
That's the basics. Be sure to check the "Terms of RUGBY!!!" section for explanations of some key words and phrases.