What is a Subnet?
Subnets are nothing but a segmentation of a Virtual Network. You can have multiple Subnets in an Azure VNet. Below is a diagram of a Virtual network with two subnets, one for Front End Servers (FrontEnd-SNet) and the other for Back End Servers (BackEnd-SNet).
In one of my previous articles Create Virtual Network (VNet) using Azure Management Portal, I created an Azure VNet called CoreLan with a default subnet also called CoreLan. Inside this Azure VNet we can create additional subnets as long as they fall within the IP range of the Azure VNet.
How to Create a Subnet
Log in to your Azure Subscription by going to https://portal.azure.com
Navigate to your VNet.
For this article I have gone to Resource Groups picked the Resource Group that my VNet is in.
Click your Virtual Network and then click Subnets
Click on the black +Subnet button
Enter a Name and Address range in CIDR and then click OK
You have now created a new Subnet in your Azure VNet