At least 100 billion galaxies are known to exist in the Universe.
Our galaxy is a spiral one, so in terms of structure it consists of galactic core and several spiral arms.
In terms of composition it includes stars, planets (made from regular matter, including atoms of all naturally occurring elements and ions), galactic gas and dust (made from regular matter, mostly hydrogen and helium as far as the gas goes, and hydrogen, carbon, silicon, oxygen and some other elements as far as the dust goes), dark matter and dark energy (there is little known about the last two).