How do I personalise themes in RapidWeaver?

Just like the title says, how do I costumize the themes in rapidweaver, like if I want to change to fonts used instead of using the default ones?
More generally, how do I costumize a theme to make it my own - I mean, to make it look like my personal style...or something.
Plus, how do I manage the CSS option in rapidweaver?
(I'm a novice so you might want to start by telling me how do I use CSS in general...).
Ever since now I've used GoLive, which worked like a text editor, so...
Thanks in advance for your help!

Check out the Rapidweaver forum: http://www.realmacsoftware.com/support/

I've been able to customize certain parts of a theme, with the help of people on the forum. I was able to insert my own images in place of theirs, and alter quite a bit of other details. The one thing I am desperately waiting for is a plug in that will make it easy to add MP3 audio files, but so far, I don't see one.