Use your default media player (Windows Media Player, iTunes) to create a mix CD from the music in your library. This is the most basic way of sharing music with a friend, physically sharing the music. Creating a mix CD allows you to personalize the music you are sharing, creating a mood or fitting a particular time or feeling.
Email the songs to your friends. Most email services allow up to 20 megabytes in attached files. The average file size of an MP3 is between 3 and 4 megabytes. Simply address the email to your friend and upload the song(s) as an attachment. Click "Send" and the music is instantly sent to your friends' inbox.
Share a link to the songs. A number of web-based music services have cropped up to create a new way of experiencing music (rather than downloading music). The user pays a monthly fee and can stream any song from the service's large catalog. Mog, Rdio, Rhapsody, Zune and Napster all offer such services for roughly $10 a month. Since the services are web-based, you can simply copy a link to a song and share it with your friend via email, instant message or on social-networking sites. When the recipient clicks the link, they are taken directly to the song's page for playback.