Bonjour, also known as zero-configuration networking, enables automatic discovery of computers, devices, and services on IP networks. Bonjour uses industry standard IP protocols to allow devices to automatically discover each other without the need to enter IP addresses or configure DNS servers.
Bonjour is a networking protocol that sends and receives network packets on UDP port 5353. If you have a "personal firewall" enabled, you will need to ensure that UDP port 5353 is open for Bonjour to work correctly. Certain firewalls will only partially block Bonjour packets, so if you experience intermittent behavior, check the firewall settings and verify that Bonjour is listed as an exception and is allowed to receive incoming packets. Bonjour will configure the Windows firewall appropriately during installation on Windows XP Service Pack 2 and above.
Bonjour for Windows includes a plugin to discover advertised HTTP servers using Internet Explorer. Click the Bonjour icon in the Internet Explorer toolbar to enable Bonjour browsing. If you have Bonjour devices on your local network with embedded HTTP (Web) servers, they will appear in the list.

The Bonjour Printer Wizard is also included and allows Windows computers to print to Bonjour networked printers, including USB shared printers connected to the AirPort Extreme and AirPort Express Base Stations. Since Apple first launched Bonjour in 2002, every major maker of network printers has adopted Bonjour. With the Bonjour Printer Wizard, computers using Windows can also experience the benefits of effortlessly discovering and printing to these Bonjour printers.