Gravity, density and bodies in test 6

I have looked at the example project Physics lab, test 6 and noticed words such as gravity, density and bodies. I suppose gravity is for physics and density is for not going through walls(am i right?) and a body creates a body made of different objects. I ran the code and found out that test 6 contains code that i would really need for future projects. Now the problem is, I dont understand the code. Could someone please explain how to use it?

Look it up in the documentation’s physics tab. physics.body creates a new physics body, gravity is gravity, and density is the density of a body in kg/m^2.

You don’t need most of the code unless you’re doing the complex examples.

See my tutorials starting at post 5 here

http://coolcodea.wordpress.com/2013/03/page/2/

Although it may be a good idea to start from the first one…