Virtual Network(VNet):
The Virtual Network is an isolated private network that supports connectivity between resources via private IP addresses.

Subnet:
This is a private address space within a Virtual Network, where supported Azure resources are deployed to. A virtual network has one or more subnets. Resources that require network connectivity must reside in a subnet.

Address Space:
Virtual networks require one or more address spaces to provide private IP addresses to resources.

How to create a Virtual Network?

Azure CLI:
Azure CLI is a cross-platform tool that can be used to administer Azure resources.

1. Create a Virtual Network
2. Create a Subnet

Step 1: Login on the azure portal with the following link https://portal.azure.com and select the cloud shell icon.

Step 2: Click on the “Bash”.

Step 3: Create a Virtual Network but before that, we will verify the mandatory argument to create a virtual network, and then we will use it while creating a virtual network.

Step 4: Like a Virtual Network first we will verify the mandatory argument to create Subnet and then we will use it while creating a Subnet.

Step 5: You can see that the Virtual Network and Subnet have been created successfully!

Note:
1. VNets supports TCP, UDP, and ICMP TCP/IP protocols. Some common protocols such as multicast and GRE are blocked.
2. 5 IP addresses are reserved in each subnet. This includes the first three and last one(x.x.x.0-3,x.x.x.255).
3. After creating a virtual network, some connectivity is enabled by default.