First let's get you excited! This is a pre-game war dance one of the perennial top teams in the world, new zealand.
What is rugby?
Rugby is a mix of elements from every sport resulting in a test of conditioning, toughness, agility, coordination, strategy, strength, and willpower as 15 people from each team go to do what cracked.com describes as: "a game where large men run at each other and then stomp on each other with spiked boots for 80 minutes."
The closest description outside of that is a game where people run the ball and tackle each other like football(minus the protective gear, forward passing, and blocking), but with the teamwork and non-stop play of soccer. The ball can only be advanced by running with it in hand or by kicking it forward.
A quick description of the rules can me found in this video:
+ Show Spoiler +
-A "Try" is scored when a player crosses into the opponents try-zone and places the ball with control in a downwards motion in the try-zone. This is worth 5 points.
-Tries are followed by conversions which is a kick from the ground through the upright goal posts. This kick is taken in-line with where ever the ball was placed down for the try, i.e. if you score by the sideline, you kick by the sideline. This ball is placed at a depth of the kickers choosing, usually farther back the farther away from center the ball was scored
-Penalty Kick - When the other team commits certain penalties they are given the option to take a kick off the ground from the spot of the infraction. If it goes through the uprights it is worth 3 points.
-Drop-kick - Anywhere on the field at anytime the player may opt to drop the ball, let it hit the ground, then kick it through the uprights. This is worth 3 points.
When the ball travels out of bounds, the game is restarted with a throw-in called a line out, formed by the two lines of men waiting to receive the ball. Players are allowed to lift their own players into the air in order to receive the ball or try to steal it
When an infraction has occured sometimes it is restarted with a scrum. This is where the 8 forwards from each team bind together and against the other team in contest for a ball rolled in the middle
When other infractions occur, the team is awarded a penalty instead of a scrum. The other team must back up 10 yards before they can come up and make a tackle. The team with the penalty may elect to kick it out of bounds and receive a line out in their favor where it goes out, kick for points from the spot of the infraction, or just run a play while the other team is back 10 yards.
So what happens after a tackle?
A player has a few options offensively when he is tackled to continue the play since it does not stop like in American football. A player is allowed one movement with the ball after he is tackled then must let go of it.
The player may choose to use this movement to make a pass, which produces some of the best and exciting plays in rugby with great continuity
One of the most important aspects of rugby is rucking to keep possession of the ball. After a player goes down, most often the other team will ruck over, which is when your teammate comes in from behind you to drive away the tackler and protect the ball by standing over it. The back of the ruck is the new line of scrimmage. The other team can fight this by counter-rucking which is when you drive the other team off the ball. This can only be done from straight behind the tackle, not from the side
Another option when you are tackled is to stay on your feet, wrapped up, while your team rallies behind you to push/drive you down the field against your tackler. Same rules on where you can come in to stop a maul as in a ruck. The back of the maul also considered an offsides line
That covers the basics, let's see something awesome!
Some great up-close offense
Some crushing hits and last ditch tackles
That's all I have for now, if anyone has anything else they'd like me to add to the OP let me know.