You need a web host. If you have 50 megs, then your domain probably came with some kind of hosting account.
A domain name is just that ? a name that points to a number (an IP address). It is not a web site or does it have anything to do with web sites beyond just pointing to the number. When someone types in a domain name, it actually just replaces it with the IP it points to. Once that happens, it connects to the web server, which sends the web site to the client (the person viewing the web site).
The web site must be hosted on a web server. For this you either have to host it yourself (not recommended), get a free one (there are plenty, but they suck), or pay for one (what most people do who bother to get domains). Since having a domain requires no space, and you said you have 50 megs, then you probably have a package that contains both the domain and the web server.
Now to set up a web site, you first have to generate the HTML code ? how you do this is up to you. There are many editors available, or you can write the code by hand (like I do) in notepad. Once you have the code, you have to get that code on the web server. This is mostly done via FTP ? File Transfer Protocol. If you have WinXP, you can just type in
ftp://www.yourdomain.com and go to file/connect (I think) and type in your username and password. If you?re using another operating system, you may need to get an FTP client. Again, many are available. They are easy to figure out and pretty self-explanatory? once you are connected, treat it just like any other folder in windows ? drag/drop the files you made onto the server, and viola, it should work!