How do you send a song through email?

The same way you would send any other file.
Once you have composed your mail then just attach the music file to it.

how do you send a song through email?

Ben's answer is correct, but there is also a copyright issue to mention here. If the song you want to send is copyrighted then it may be illegal to do what you are asking. Copyright law allows you to make copies of copyrighted material for your personal use ONLY. Giving a copy of the song to someone else is a violation of the copyright.

If you're sending to an Outlook Express addie you can send music as background, then they're only listening to your music while they read the e-mail. DavidB.

Personally I would NEVER send someon an e-mail that played music without permission. One never knows where one is going to open that e-mail or how loud there speakers might be.