Spirals are catagorized by how tightly wound the spiral is, and how big and what shape the central bulge is. S0 galaxies have a disk and a large central bulge, but no signs of spiral arms. There is no disk structure. The stars mainly orbit radially. The lack of gas means that no star formation occurs.
Irregulars are gas rich but often metal poor.
Star formation has been slow and inefficient. The Milky Way is part of a small cluster of galaxies called the local group. There are other small to moderate sized clusters nearby. The nearest big cluster is in Virgo. It is roughly 20Mpc away, and 2Mpc across.