1. By default, the OS X firewall blocks iTunes sharing, so if you're running a firewall, you'll need to enable this feature. On the computer that hosts your iTunes library, launch System Preferences. (It's in the Apple menu), select Sharing, click Firewall and check the iTunes Music Sharing box.
2. In iTunes, enable sharing: Open preferences, click the Sharing tab and chec the "Share my library on my local network" box. Share your entire library or only selected playlists. You can also specify a password to limit access. Click OK to confirm your preferences. iTunes reminds you that "Sharing music is for personal use only." Click OK.
3. Once you share your library it should automatically show up in the iTunes source list for all networked computers. If it does not, open preferences on that computer, click on the Sharing tab and make sure that "Look for shared libraries" is checked. Click OK.
Shared libraries are only available on your local network, so your friends in other countries won't be able to stream your library using this method.