Looking from the nock down the shaft, if the front of the feather wraps to the right, it is right helical. Front wraps to the left, it is left helical. There is also straight fletch, right off-set (front of feather right of shaft center line looking from nock down the arrow) and left off set (front left of centerline).
Feather types: looking from the back of the feather to the front with the base down, on right wing feathers the natural feather top is on the right, the base foot extends to the left. Left wing the natural feather top is on the left and the base foot extends to the right.