If you only have one server, or aren't likely to need two or more of your Mammoth Cloud servers in the same location to have a private connection between them, you do not need a VPC.
Virtual Private Cloud (VPC) is a technology that allows you to create your own virtual network within Mammoth Cloud, that isolates your cloud servers on their own private network.
Each VPC has its own private IP address range that you select during creation, such as 10.240.0.0/16. Because the virtual network is dedicated to your use, you may use whatever IP address range you like.
Please note: a VPC does not provide a VPN endpoint by default. If you need VPN connectivity into your VPC, you will need to create a VPS to use as your VPN server/endpoint within the VPC.
A VPC information page with example use-cases is available here.
There are two VPC guides available here.