This is my first site, and I had absolutely no knowledge of HTML or CSS when I started. It's all been trial and error, and I could use some advice.

My biggest mistake was not learning HTML and CSS before I started. I built the site with Dreamweaver, using video tutorials from the web. I made a lot of "uneducated guesses", took some chances and, somehow, the site seems to work.

I am going to rebuild the site from scratch after I learn HTML and CSS, but I need to keep my site up and running during this process.

My HTML has been validated (although it is probably very sloppy)
My CSS, however, has some problems. If someone could look at my CSS and tell me if I have made a terrible mess of it, or if I simply have a few fundamental problems, I would greatly appreciate it.

The URL is http://www.themonumentartist.com

Thanks again.

The only thing the validator is griping about is that script inside your css file. It doesn't belong there, it belongs in your page. The only thing that goes into a css file -- is css rules
You also don't want the <style></style> tags in there either.

Other than that, the css isn't too bad. Learning some css shorthand will clean it up once you get the hang of it. CSS shorthand will turn this:

margin-top: 10px;
margin-right: 10px;
margin-bottom: 10px;
border-top-width: thin;
border-right-width: thin;
border-bottom-width: thin;
border-top-style: solid;
border-right-style: solid;
border-bottom-style: solid;
border-top-color: #471812;
border-right-color: #471812;
border-bottom-color: #471812;
border-left-color: #471812;

into this:

margin: 10px 10px 10px 0; (TopRightBottomLeft - think TRouBLe )
border: 1px solid #471812;

Thanks, LnR, for the help. I removed the script and the <style></style> tags. Now the validator finds no errors. It does, however, show 34 warnings, all of them seem to involve colors. Is this something that I need to worry about?

No, nothing to really worry about. The validator apparently looks for background and foreground colors defined on everything, not always necessary IMO.

By the way, your work is amazing !

Thanks, LadynRed, you just made my day!