I used to play rugby. Three years in college. It was outrageously fun. I also played second row. You will have the following jobs: You are going to be in the middle of the scrum. Tape your ears on tight, and if you work out, spend some serious time on squats, as you will be the driving force. If you get your butt low (below your shoulders), you can really generate some leverage and drive the scrum. If you get your butt high (above your shoulders), you will generate little power, and cause yourself serious back pain.
The reason that your height comes into it (I am 6' 3") is that you will also be responsible for winning the ball in line outs. When the ball goes out of bounds, there is a line out where the forwards (including you) will line up perpendicular to the sideline, opposite your opponents in a similar line about 2-3 feet away. Then a person from the team that did not touch the ball last will throw the ball down the middle of the two lines (between the two teams), and you will try to catch it. Your height is a huge asset in this, as it works out to be something remotely like a rebound in basketball. If you catch it, your teammates on either side of you will "bind" (grab) on to you and protect you from the other team, which will try to take the ball from you. Or vice versa, if the other team grabs it. There is strategy as to which team is throwing it in, and signalling to their teammates how far the throw will go, but you get the idea.
Lastly, as a forward, your job will to be to tackle the opposing teammates, and get your head in there everytime you can to help win the ball for your backs, who will do most of the running. It's best to get some nasty attitude

going, because you are going to be "in the trenches" -- winning possession of the ball, pushing the pile, tackling opposing players, etc.
Sometimes you will get the ball yourself coming out of a ruck or maul. When you do, you can either pass it to your speedy backs or run it yourself. If you choose the latter (if you're near the try line, or have some open field), then channel Larry Czonka, and run the heck over whomever is trying to bring you down. Make them pay. It is always better to hit someone than to be hit.
Rugby will make you sore, but I've seen far worse injuries in football, where the collisions can be more severe, and the helmet can become a weapon. Have fun. It's a blast, and a great way to relieve stress. I miss it.