It's pretty simple!
First you have to find a place to upload your songs; a filehosting service. The most popular site is
YouSendIt if you don't mind it expiring in 7 days or 25 downloads (whichever comes first). Some other great alternatives are
Sendspace,
Rapidshare, and
Megaupload.
Uploading the file on any of those sites is very easy. Just enter in the info (usually your email address) and browse through your files to select the one you want to upload. Then it's just a matter of waiting for the upload to complete. Once it's done, the site should tell you that it's finished and give you a download link. Copy the link and voila, it will direct anyone to the file you uploaded.
I hope that wasn't too confusing.
(By the way, chibi_sunny, that's a cute graphic you have there, did you know you can go into your control panel and put it in your signature, or upload it as an avatar (under your name?)