At the beginning there is no rotation. The cloud may start with roughly uniform density along with some momentum. Over time, this density becomes higher in the

At the beginning there is no rotation. The cloud may start with roughly uniform density along with some momentum. Over time, this density becomes higher in the middle and lower around the outside. Everything in the cloud begins accelerating toward the place of higher density which forms into the sun while at the same time continuing in the direction according to its initial momentum. This is what causes rotation that leads to the formation of a disk. Any time you have momentum in a direction other than the local centre of mass (star, planet, etc), your path of travel curves into a circle (actually an ellipse, but that’s another topic: see Kepler’s laws).