You can share music in your iTunes Library with other Macs with which you are networked. You can also listen to music that is being shared with you.
To share your music with other Macs on your network, you just need to set your sharing preferences:
Open the iTunes Preferences dialog box and click the Sharing button.
Click the "Share my music" radio button.
Click the "Share entire library" radio button to share all the music in your Library, or click the "Share selected playlists" radio button and check the box next to each playlist you want to share to share only those playlists.
Give your shared music a name by typing a name in the Shared Name field. This is the name of the source others will select to access your music.
If you want to require a password for people to be able to share your music, check the "Require password" box and enter a password in the field.
If you required a password, provide it to the people with whom you want to share your music.
After you have shared your music, people can access it using the same steps you use to access music being shared with you.
For your music to be accessible on the network, your Mac must remain awake. If you turn it off or it goes to sleep, others won't be able to access your shared music any more.
To search your network for music being shared with you, open the Sharing pane of the iTunes Preferences dialog box and check the "Look for shared music" check box. When you close the Preferences window, iTunes looks for any sources being shared with you. When it finds them, they appear in the Source pane. Shared sources have a blue icon with a single note symbol. Do the following:
Select the shared source that you want to listen to.
If it requires a password, enter the password at the prompt and click OK. The shared source becomes available.
Click the Expansion triangle next to the source to see the playlists that have been shared with you.
Listen to the shared source just as you listen to your own playlists.
You can't move music from a shared source into your Library from within iTunes.