The HooToo can bridge a "Wired" network or a "Wireless" network.
Without getting too technical (I hope anyway) computers on the SAME network are generally considered "Trusted" and as such the security is lower. So a computer on the Wireless Network at a location, can generally see another computer on the same network easily and makes it a much easier target for hacking. (Think of a vault at the ban with the safe deposit boxes. If you can get into the vault, you can see ALL the boxes. You are half way to the prize, if you are a hacker)
Adding another "Network" through the HooToo, gives you a virtual "Separate" network (Kind of like a vault in a vault).
Communications going out of YOUR network would still have to go out to the Public WiFi and can be seen, but if you use Secure sites (those that start with https:// ) then you have encryption. Just like if you go out of the Vault (in a vault) you can be seen, but encryption is like a disguise.
Have you ever used a Public Wifi that makes you "Agree" to the terms or has a login page? (Hotels, Hospitals, etc...) the HooToo can be set up to do that ONCE for you and then all your Wireless devices (laptops, phones, tablets, etc...) don't have to do it. They just connect to the HooToo and the HooToo connects to the public WiFi. Another advantage is that you don't have to keep changing the WiFi Access key on all your devices. You set them up to Automatically connect to the HooToo and when it's available, your devices can use it.
The HooToo will also bridge a WIRED network too, like Ed has described. There can also be a cost savings too if you get one "Free" connection and have to pay for others, or even if you have to pay for "EACH" connection. WIth the HooToo, you pay for ONE connection and share it with all your mobile devices. In the "Wired" mode (Wire in but only wireless out) it acts as a routers (slightly more secure). I have read though, that a firmware upgrade (or software on the USB) can allow it to be a Router in Wireless in Wireless out mode too but I don't need to go to that level so I haven't explored it.
Finally another nice thing is I can hook up a usb flash drive with things like movies on it. The kids in the back can then stream their own favorite movies directly from the HooToo and USB drive to their devices. With a 32GB Flash Drive, I can get several hours of movies for them to watch hopefully keeping it quiet for the drive. (well with headphones for them)