Yeah I see what you mean, I only think they look very similar from above....
But from the side, they are totally different. But I still don't get how galaxies are made to look as if they are spinning by gravity? Or are they spinning? And how fast are they spinning?
The galaxy itself does not spin. It's not a rigid body, it's a collection of stars and gas which orbit the centre of the galaxy, just like the planets go around the sun, the stars and gas orbit the centre of the galaxy.
The spiral arms in a spiral galaxy are not a solid structure. The spiral is caused by spiral density waves. As stars orbit the the centre of the galaxy, some stars gravitationally tug on stars passing by, it slows down the stars passing by temporarily. Due to this, some places become clumpy for a while. Over time these clumps cause spiral pattern to appear in the galaxy. The spiral arms winding down is just an illusion. There are no arms winding down, something you'd see if the arms were a solid structure. This is a hard thing to grasp, for more on spiral density waves, copy and paste the link in the parentheses to address bar (bit.ly/cjNWzp).
How fast something orbits the galaxy depends on a few things, but mostly it depends on how far away something is from the centre of the galaxy. In the milky way, the sun is about 25,000 light years away from the centre of the milky way. It orbits the milky way at about 200 km/sec. Stars near the centre of the galaxy orbit at speeds of more than 1000s of km/sec.