There are three kinds of Galaxies, Spiral , Elliptical , and Irregular . The only difference between the three is what shape they are. Galaxies often crash into one another. Even our own galaxy has had others pass right through it. Don't worry though, galaxies can pass through each other quite safely.
Stars are so far apart that the chances of two colliding is nearly impossible.
Their long twisting arms are areas where stars are being formed. The spiral arms seen in this kind of galaxy are circling waves, much like the ripples of a pond. These waves cause new stars to form. Some of these new stars are very large. Because of their big size these large stars glow brighter than their smaller cousins.