so will your disc turn left or right during the roll? or does it only do it at the end?
That depends on a) the angle your disc hits the ground at, b) the speed at which the disc is travelling when it hits the ground, and c) the stability of the disc you're rolling with.
If you're throwing right-hand back-hand rollers, then typically speaking, the less stable the disc, the faster it will turn over to the right while rolling...also, generally the faster it's travelling, the quicker it will turn over.
You'll want to start off with something understable...I learned with a Valkyrie and currently roll very beat Eagles, but any understable driver will work. I'd recommend something slower when starting off (Polaris LS, Leopard, L-mold Eagle, etc) simply because they tend to hold the release angle longer than faster drivers. Focus on releasing the disc with anywhere between 30 and 50 degrees of anhyzer and
following through on the same angle...the follow-through is key in keeping the disc on the same angle from your hand to the ground. Getting your disc to hit at about a 45-degree angle will generally yield a good roll...once you get the hang of it, though, you'll be able to experiment with different angles to find what works best for your particular discs and the shape of the fairway you're trying to roll on.
When starting off, it's easier to learn rollers that hit the ground relatively close to you. Once you get used to the shot, you can work on throwing sky rollers (where the disc travels a good distance before hitting the ground). Sky rollers will typically yield more distance, but they're a bit trickier to learn...since the disc is in the air longer before making contact, there's a larger chance that it will change angles between the time it leaves your hand and the time it begins rolling.
I'd recommend working out the basics of the shot in a wide-open field with lots of left-to-right distance to work with. Chances are your first several attempts will either shoot way off to the left or right.