Looking for a better explanation of Grid objects

Having trouble getting a good understanding of the Grid object.

I see them in the example, but quite getting the positioning, width and height stuff.

Also, done a lot of web design, and it was easy to just add a border to tables or elements, to see what is happening.
Is there any way to do this?

You can add a background color to any element. It is probably the easiest way to see what is going on.