hi triscuit,

space junk is a somewhat advanced example, since it uses a class and is 3D.

with regard to your questions:
• the for loop in setup() is used to create (or more precisely instantiate) the cubes (as object data in memory only)
• the for loop in draw() draws the cubes
– if I only created one cube, I wouldn't need the for loops, as they are just used to process the multiple cubes.
• in general the color coded stuff is part of the language, not the stuff the user defines.
• the mouse position (only x component) is just used for the z argument in the translate(x, y, z) function call, which zooms in/out as you move left/right.


If you're really new to this stuff, I'd suggest working through the examples in the basics section and spending some time exploring the language reference.  You might also want to pick up one of the/both Processing books, which explain in detail about things such as variables, loops, etc.

have fun.
ira