Similarly to what AP said, think of it as a 'pooled' environment. With Essentials Plus, you're entire 'pool' of ESXi servers can use up to 6 physical CPUs and 192GB of RAM. It doesn't matter is 1, 2, or 3 servers are utilizing those resources (although Essentials Plus does limit you to a max of 2 processors per host).
vRAM is simply how much RAM your powered on VMs are using. If you have 5 VMs, each with 8GB of RAM, they would be using 40GB of vRAM (assuming they're all powered on). If only 1 VM is powered on, it is only consuming 8GB of vRAM.
vRAM is really no different than licensing processors, except in vSphere 5, you have to license both vRAM and sockets. This change was obiviously met with a fair amount of criticism... Just see some of the licensing threads with thousands of messages...