websites use, at the core, HTML. HTML(Hyper Text Markup Language) is a tag-based language, that is used to tell the web browser (IE/FireFox/Chrome/etc) how to display text.
Most of HTML's formatting has been deprecated for the strength and ease-of-use of CSS (Cascading Style Sheets), which can use either a separate style sheet file (.CSS) or in-line styles (something like: [
text here ]
If you're new-ish to this sort of thing, you'll likely want to tackle it either from a Dreamweaver orientation, using drag-and-drop methods to craft a site, or from a Photoshop orientation, drawing a site as an image, and having Photoshop cut it up into many little images to be used as a site.
Either method isn't for the faint-of-heart, and I'm not sure if there's another way. :P
At that point, you have your site, but it isn't hosted anywhere. You need to host it somewhere for people to see it. Sure, it's possible to host it from your computer, but you'll eat up bandwidth and likely get your internet service provider mad at you, if not boot you from them. Also, if you host it on your own PC, your PC must be on at all times for people to access it. So, instead, there's hosting companies out there. I'd recommend http://www.arvixe.com - they're awesome-sauce.
*Edit:
Oops, forgot to mention a few things. ^_^
AFTER you have a host, you still don't have a domain-name ( like google.com, aol.com, myspace.com). Without one of those, your internet address is something like 123.456.78.9, or similar (IP Address). With a domain name ($11-$20 or so a year, depending on registrar), you can have a friendly name for people to remember.
Now, after you have *THAT*, you can worry about marketing. You can either tell friends, and have them tell friends, etc, and you'll want to submit your site to google. Google has a whole section devoted to webmasters, check that out in your spare time.
With Marketing, you can look at two major pay-schemes for your campaign: Pay Per Click and Pay Per Impression. The first favours you paying a small (fraction of cents) fee for every time someone clicks on a link or banner that takes them to your site. The second, favours you paying a small (fractions of cents, again) fee for every x amount of views of said banner/link (usually around 1,000 or 10,000). Of course, if you design the banner yourself, you'll want the first option - you'll pay for what you get. If you get a super-awesome, high-action banner, you'd opt for the second option, as you can imagine most people out of a large crowd will click it, and it's usually cheaper per impression than it is per click. :P