How do motors work?

In physics, we're learning about electric motors and we had to look up a simple motor that we could create and answer questions that came along with it. The motor I found to build was really simple. You take a paper plate and tape 2 paper clips on it to...

create a stand sort of thing for a coil of copper wire. I stripped the wire at the ends where it would rest in the paperclips and the directions told me to color one side of one of the ends of wire black with a marker. What's the reason for this?
And then to make the motor actually work, I put a magnet on the top and on the bottom of the plate between the paperclips. I hooked up the little motor to a 9V batter, and it turns. I'm just really wondering what the black marker does. And I'm also wondering what would happen if I made the loop of wire smaller or larger, like if it would move a different speed.
Thanks in advance.

I think the black marker is to create a point of reference- so you can easily see that the plate is turning. changing the length of wire should I believe change the speed- also changing the 'guage' of wire will change things up too.