themes- how to?

hi i’m new to wordpress and utterly clueless. i know how to install themes and such, but i have no idea how to go about customizing them. i installed wordpress after visiting this site- loveisdead.net. she uses wordpress and her layouts are awesome. i just want to know how to customize them so they look like that, with my own colors/graphics/etc. any help at all is much appreciated. thank you!