What is the difference between private and public VNET in azure cloud ?
It’s not just Azure, it’s all cloud providers. They just have slightly different names for it. Azure - VNET, AWS - VPC/Subnets
Public networks have inbound/outbound access to the Internet. It’s where you put public facing servers and load balancer endpoints.
Private networks are not directly accessible from the Internet, and only have outbound access via NAT gateway devices. This is generally where most infrastructure should be placed to reduce the attack surface. Your servers that are behind a loadbalancer would go here, along with DB servers and other services that should not be directly reachable from the Internet.