Because the collapsing cloud is rotating, the collapse is inhibited in the plane of rotation. The gravitational collapse is uninhibited along the axis of rotation. The result of this asymmetric collapse is a flattened disk that is rotating around the central protostar.

The above is a picture of a circumstellar disk.

To see a movie simulation of a disk forming around a protostar, click here.

This is a graphical model of the disk formation process described above