ACI Virtual POD allows you to extend your ACI Fabric to a remote location through a IP Cloud. If you have bare metal Servers with ESXi at a remote location, you can uplink those servers to routers at remote site and then install a pair of Virtual Spines, a pair of Virtual Leaves and Cloud AVE and you just added a new pod to your existing fabric at a remote location. Now you can stretch your Tenants, VRFs, BDs, EPGs across to the remote virtual pod from APIC with same policies.
Use cases are generally for extending to bare metal private clouds and Colo facilities.
This guide will step you through installing Virtual POD step by step in a practical fashion.
Try it out in your lab and see how you like it