heres all the details i found out while doing it my first time..
you can kinda see that the roller is on a hinge and that there is a hinge down by the hub. the top one angles the roller up/down/out in relation to the fender. You want to start with it pointing more upwards to start the roll. then you can adjust it to face outwards to get the lip flush with the back of the fender. then angle it a little more up if you want to pull the fenders out a bit.
Basicaly, lots of heat and go slow. that way you dont end up with this..cracked paint.
i just jumped on it with a mere understanding of what i wanted to accomplish. ive rolled three cars so far and none have had any paint chipping. so just make sure to go slow, do a small part at a time, and use a heat gun to save the paint.