Configure vmbr for the first time, help!

Hi, i installed Proxmox 3 for the first time, the installation works, i view correctly the web console but now i have to install 2 machines, both of which must be reachable from the outside, in which to install the web server and db server. I read in the guides that i have to configure the network interfaces (vmbr) but do not know how to do. The Proxmox server already has a fixed IP address, to have 2 more virtual machines I have other 2 fixed IP addresses? Otherwise, how can i connect to virtual machines via ssh or the web?

Thanks