Gtk, Qt etc.

I'm confused about gtk.

gtk2, gtk3 and qt. none of the parts make sense to me.

What I like to do, is to install a theme, and icon theme. I would like to configure this. Eg. I want to change the colors and icons.

So first of all, what do I need to install to make my gui apps look good? Should I install a gtk2 or gtk3 theme? and what about qt? I would like to avoid installing a gtk engine, and would like to configure theme and icones, in the gtkrc itself or something similere. I use a tiling wm if it is realevent to know.