Any time there is a breakdown of play without a foul being committed there will be a scrummage.
Just like US Football, the forwards of a rugby team are the combined offensive and defensive lines. You've seen a scrummage - it's very much like a scrimmage except the lines lock together. Here's a quick badly formatted illustration of a scrum formation:
Front row L->R: Prop, Hooker, Prop
Second Row: Flanker, 2nd Row, 2nd Row, Flanker
at the back: No.8
Instead of the ball being snapped to the QB, the rugby equivalent (the scrum-half) of the team awarded the "put-in", er, puts the ball into the scrum from the side. Each team's Hooker then tries to, er, hook the ball backwards, through the rest of the forwards, until it gets to the No8. The scrums will be pushing against each other to gain ground during this time.
Anyway the ball arrives at one or other of the No.8s, it's then collected by the scrum-half again who then feeds it to the backs via a lateral pass and open play recommences.
The "put-in" must be straight down the middle tho spin is allowed to give your team an edge. It's perfectly possible for possession to turn over in a scrummage and it often will if one set of fowards dominates the others. It's also acceptable to keep the ball in the scrum and drive it forward but that runs the risk of collapsing the scrum which will usually result in a penalty.
Other than that it's 5 points for a try (ball MUST touch the ground not just cross the goal-line plane) and 2 points for a conversion (the kick after). You can also score 3 points for a penalty kick and 3 points for a drop-goal. A drop goal can be attempted at any time by any player and is essentially what you would know as a punt, except that the ball MUST hit the ground before being kicked. This makes it quite a difficult feat which is why you don't see them happening every time a player is in range of the posts.
Other general ramblings. . .umm. No forward passes are allowed. Any kind of forward movement of the ball unless its a kick is a foul whether the movement was intentional or not (so a dropped pass will usually push the ball forward and be a foul and so will an attempted kick that comes off your shin or whatever). Offside rules are arcane and beyond the scope of this forum. You are not allowed to play the ball from the ground (if you're on the ground) and if tackled you must release the ball. If the ball goes out of play at the sidelines there is a "lineout". The team awarded the line-out chooses how many forwards are in the lines, the forwards line up next to each other facing the sideline and the scrum-half throws the ball in from touch. The enormous forwards then leap for the ball and try to get it to their backs and open play resumes.
Phew. Need any more? Just ask
