You don't use the virtual network editor for bridged networks.
In fact you rarely need to use it at all, because most of the time it just does what is necessary. It is for providing a Nat'ed network for virtual machines.
A bridged network adapter will alias your host machine's nic and put your virtual machine on the same network as your host machine. It will obtain an ip from what ever dhcp server gave your host machine it's ip.
You need to decide if you want your virtual machines on your main network or on a Nat network "behind" your host machine.