The youngest galaxies are generally the ones furthest away, so harder to study them. How did the gas collect together, given that there were no winds or supernova explosions or the equivalent to force material together to become gravitationally bound. Lots more questions, lots more research going on. As usual, start with what's obvious. In this case, we start by classifying galaxies by how they look.
Spiral galaxies are the ones like our own Milky Way.
Flattened, with central bulge and halo. Spiral arms, some well-defined, some more patchy. Because of the younger stars in the disk, it looks white or blue when we take images. The bulge, with older stars, will look red or yellow. Also lots of dust, ionized gas, neutral atomic gas, and molecular gas in the disk.