Skinning wordpress

Hi,I’m new to WordPress but not development, I’ve heard really good things about the community here so thought i’d expand my knowledge of WordPress. I have used it briefly before, but nothing major. Basically, for me, i’d like to skin it so I can just add my own custom CSS to it and use it as a framework for content management. What’s the best way to go about this. I don’t really want to go around messing with things that I don’t really understand yet, although I can program in PHP well enough.

But I know people already skin WP so I thought I should ask some pros about the best ways to do it.

Thanks for your help,

Jonny