Creating your own layout

I was wondering what scripts you would suggest I make myself familiar with if I want to try to design my own templates and layouts. I hired someone to do what I have up now (http://www.kissmegreeneyes2.com/blog) but I’m used to designing my own sites and frankly I can’t afford to pay every time I want to make a change. I’m usually very good at teaching myself how to do things but I’m really at a loss as to where to get started. As I mentioned before, I’ve made my own pages before but I use FrontPage (I know… I took the easy way out) but now I’m wanting to learn the scripts so I can expand my capabilities. I’m pretty familiar with HTML and I’ve used some php but that’s about it. I’ve never played around with style sheets, CGI, perl, or anything like that. I’m good at following directions and I catch on fast. Normally I can figure something out just by looking at it but with WP, it’s different because it seems as though this file calls up another file and they’re all nested and layered… Would all this make more sense if I read up on php and learned the basics of that before trying to jump directly into manipulating script in WP? Any tips, suggestions, or links would be helpful and I would appreciate it very much.