I can't teach this here but as you are creating the server you will learn a great deal along the way.
In short, a VPN server can be many things to many people. It's sort of like "I want ice cream." So many flavors.
Hello, I want to setup a VPN server in a raspberry pi in my Lan.
My requirements are the standards that any VPN server provide.
My question is if is that possible to be considering that that server and the clients are under a router, under the same external IP.
My thoughts deploying it are that clients will attempt to connect to the server via a service like noip domain name that maintain my IP
Is there any problem to deploy it?