How to transfer my html/css home page into Drupal?

Hi

I'm not a sophisticated coder, but I know html and a decent amount of CSS. (I worked as a Director in non-profit and due to lack of finances and time, became "OK" at webdesign"). I have designed "regular" webpages before, - the home pages were just html with CSS.

I've inherited a website set up by someone else on drupal, which I don't know at all. It's not well designed graphically and has lots of coding errors in CSS etc. I've designed a new homepage just flat html/css and would like to see how it works in Drupal.

Problem is, I can't figure out how to make it display as a "theme", or, if easier, to adapt an existing theme to show what I want.

I've downloaded drupal onto my computer to play with, so I'm using http://localhost . I'm using the Apache bundled xampp.

I've been told drupal is really fantastic and "easy to use". Can anyone help me by giving me "easy instructions" how to get my home page (html, css style sheet and a little flash) showing in it?

Thanks:)

Jonathan