Creating Basic Chassis

[Apeace]

So, I am not very experienced with Inventor. But what I want to do is be able to create a simple design for a basic drive train idea. I took a 45 min session in December, but I can't remember everything they taught.

Basically, I created a 2D drawing of my robot. Then I remember the teacher telling us how to turn the lines into materials. We used aluminum for the material, but I can't remember how to turn it into anything. I know we didn't extrude the lines, or if we did it made them around the lines. It basically became a simple looking design for a chassis.

Once that was done we could connect corners and such, but I can't remember how, and it might be different in the 2013 version, so I'm not sure.

tl;dr I don't know how to turn sketch lines into basic parts. I don't mean extruding, I mean like it turns the line into a long hollow rectangle around the lines.

Any help would be appreciated.