[Cidermaker]

Stars and planets (and galaxies) spin because they form from large clouds of matter that collapse. These clouds of matter are made up of blobs (a technical term) that have more-or-less random motions. The net spin (angular momentum) of these will not be zero. That is to say, the net rotation of the cloud will not be zero. As the cloud collapses to form a more compact object, the spin (angular momentum) is conserved, which means it has to spin faster as it gets smaller. This is just like an ice-skater who spins faster when he brings his arms down to his side.