There are 3 types of networks (virtual switches) you can create in Hyper-V: External, Internal and Private. The External type is the most known and used, as this lets the VM access a physical NIC on the host, giving it access to a physical NIC, e.g. its own dedicated ethernet device with a gateway to the Internet. The Internal type can be added to create a local network between other VMs running on the host, as well as the host. The Private type creates a local network between the VMs on the host, but not the host itself.
Example IPv4 configuration of HOST (virtual) NIC
IP: 192.168.1.1 MASK: 255.255.255.0
Example IPv4 configuration of VM1 NIC
IP: 192.168.1.2 MASK: 255.255.255.0
Example IPv4 configuration of VM2 NIC
IP: 192.168.1.3 MASK: 255.255.255.0
VM1 and VM2 can now communicate on both Internal and Private networks. As well as with the Host on Internal network. (If you try to ping without replies, it may be your firewall blocking ICMP packets).