It's four products in one.
- Base Station: Plug in your local network or cable/DSL modem, then configure it to share internet around your home or office.
- Remote Station: Use it to extend your current wireless network, or to bring wired internet to places not wired. It works in the reverse of the method mentioned above, and requires an existing Airport base station… whether it be a regular Airport or another Airport Express.
- Wireless/wired Print Server: Plug in your printer, and have it shared to all compatible machines on the network. (even Windows machines with the “Zero Config Wireless” service enabled can see them) It does this in addition to the things above.
- Wireless Audio link: iTunes connects and streams audio through the built-in Optical/Analog Audio-out port.
I installed one near my TV and game consoles, then had my existing Airport Base Station automatically configure the new, Airport Express. They talk securely over the air, while the new Airport Express provides a media link from my Mac Pro or MacBook to my stereo, and it also provides an Ethernet port for a Tivo or for online play with Xbox or PS2.
I was very skeptical at first, but it's definitely a great product.