How does a beginner make a theme?

I've been using Xaraya for a few weeks now. I've got the hang of the 
very basics and it looks like if I want to do much then I will have to 
make a theme with the visual layout that I want.

How does a beginner go about this? I have no idea of what to do.

What is the first thing that I should look at?

Does this involve using the built in functions of Xaraya or does it 
require some coding?

SpiritTech