How should I send a mp3 or video song through email.

As an attachment, but most, if not all email clients have a size limit on attachments.

Correct and Don't sent to many at once as the Attachment, Special if they are on Dial up, Takes to long to Download emails that have big file attachments, and can stop the download of emails altogether.

If this Helped Rate it.

Also, you have to be concerned about copyright issues. If this is commercial copyrighted music, then you are doing something illegal.

Some email websites won't let you upload a video or mp3, if that's the case just zip it. Again though, you shouldn't if it's copyrighted material.