Marconi, forget everything you know about other CMSes. There’s litereally several ways to reach the same end goal. You can make your
CSS be a document, which opens up interesting things programatically. That’s probably a bit advanced for starting out though.
You can also just stick it on the filesystem, which is what I do 99/100 times. Typically I’ll put my "site.css" files at the top level of the assets directory, so that getting to any images can be done with succinct code:
#foo { background: url(images/bar.jpg) no-repeat 50% 50% }
Then in my templates I stick this at the top of my head section immediately after my title tag and any meta content:
<base href="[(site_url)]"></base>
<link rel="stylesheet" type="text/css" href="assets/base.css" />
<link rel="stylesheet" type="text/css" href="assets/site.css" />
The "base.css" file is your typical reset similar to what Eric Myers recommends. The reason I don’t like to use the templates folder is that it just sticks everything yet another level deeper in the filesystem and I’m a lazy typer.