If you are looking for info on demo hosting (since FAWM does not host actual MP3 files), look here: demo hosting.
Shareware Music Machine maintains a large list of music software, including soft-synths, VST effects, VSTi and other software instruments, sound recorders, and so on. Visit their site at http://www.hitsquad.com/smm/.
If you're posting music here, you need to find some way of getting sound into your PC. And there are LOTS of ways to do it.
And, of course, you probably need a microphone. You don't need to spend a lot of money on a mic. And if you're JUST going to use a mic, you can look into a USB mic, which can negate the need for any other recording interface. You can buy a USB mic for as low as $25. An excellent traditional mic can be had for under $100 (and a decent one for under $30). You'll probably need an XLR cable, and it's not a bad idea to think about a pre-amp. The two types of mics you'll want to look at are Dynamic Mic and Condenser mics. Dynamic mics are more versatile and better for live performances, while condensers can be much better for recording.
Once you can get sound into your computer, you'll probably have to spend a little bit of time trying to set up whatever software you're using, and you'll be best served by hitting google for details there.
As you start getting a little more advanced, here are some more terms to learn:
Well, you need to publish it somewhere, preferably in a format people can listen to. Chances are that you've recorded your song in one of the programs listed above. There should be an “Export” feature there. That'll probably give you a WAV file (if you have a PC) or an AIFF file (if you have a Mac). Convert that to an MP3. (There are lots of ways to do this, but the easiest is probably just using iTunes to convert it.)
Now, you need to put your file somewhere where other people can get it. Fortunately, there's a great section about that in the File Hosting section of the FAQ. Enjoy!
Key to ANY remote recording collaboration is setting the parameters ahead of time. There are any number of methods and techniques that will get the job done, and long as you and your partner(s) communicate.