Galaxy is a large group of a stars, that have it's form because of dark matter ring.
spiral galaxies are galaxies, that have form of a spiral, consisting mostly of stars and interstellar gas. Every galaxy rotates, but spiral ones, are galaxies, where rotation is noticable.
Spiral with jumper Edit
theese galaxies, are quite similliar to nomal spiral ones, but the difference is in the center, that "jumper", like in our host galaxy.
elliptical galaxies, are galaxies, that doesn't have spiral form, instead of it, elliptical galaxies have form of ellypse (circle, oval, etc.).
irregular galaxies, are galaxies, that doesn't have any form. Irregular g. are mostly looking like huge nebulas with stars inside it.
core of a galaxy, is a part, where globular star clusters and black holes are located. There is also galactical core black hole (Sagittarius A* in Milky Way, for example).
Mid zone Edit
there is much mid aged stars. Our sun is located it mid zone of Milky Way.
Outer zone Edit
there is less stars, mostly, there is interstellar gas.
main article Paragalaxy.