Looking for info on screen layout

I bought a template and am trying to tweak the layout. The theme I bought has modules, which I can move to the left, right, top etc. The author created a bunch of 'banners' - everything seems to be a banner - why banners as opposed to anything else? Is there a reason for this, or is this just how he does it?
Also, for example, Best Sellers is a narrow-ish column on the left, but when I move it to the right it becomes much wider and distorted. I assume it's because its set up to be only a 2 column site? And that the widths come from the CSS? But I am guessing and don't really know. And how would I theoretically create a 3rd column if I want it to be even more to the right of the second column? Can anyone suggest a good way to understand it or read about it (I think I'm talking about the connection between the layout you see on-screen and how it ties in to the underlying admin panel and css)? If I can understand it I'd try to make a visio diagram for other noobs that are at my level of dumbness...

I would suggest you direct these comments to the person you purchased the template from. As far as learning on layouts of the site, you can use the demo and play with it to learn how. That is what I did. You can play around with layouts, modules, etc to see how things interact.

But when it comes to templates that you purchase, and not the default ones, then you should receive support from the author. just my opinion.

ok, like I said, this is probably a dumb question but for example, I have Bestsellers and Latest modules. They both have the same settings in modules (Layout=home, Position= Column Right, etc). But Bestsellers has the products going up and down, whereas Latest has the products going left to right. What determines that? Is that css or tpl ?