This is an edge-on picture of the Milky Way, the galaxy in which we live. This is not an actual photograph of the Milky Way: since we're inside it, it doesn't look like this to us, and it is far too large for us to have gotten a probe outside of it yet. Instead, this is a reconstruction from background radiation.
The Milky Way is what is called a spiral galaxy. This image is from the side, instead of above, so the spiral structure doesn't show. As you can see, most of it is roughly the same thickness, but there is a large bulge in the center.
A spiral galaxy like ours may contain billions of stars, and may be 30 kiloparsecs across--that's a billion billion kilometers. Spiral galaxies are one of the most common types, making up about two out of every three bright galaxies.
PtyS 105 is the PtyS course with the most to say about galaxies.