You can use Android VPN for Port forwarding. But that info is all for router hardware. It is a very important way to let the service on the computer that behind your router can be accessed by users from internet. Router is playing a role of forwarding data between your computer and internet here. Sometimes, a software will do the same thing too. It will bridge communication between client and server sides. We can call this kind of software as port forwarding software.
For example, you have a computer A and VNC client is installed on it. You want to use the VNC client to access VNC server that installed on computer B. But unfortunately, computer B is located in a private LAN. That means computer A can not directly access the VNC server on computer B. The easy solution to resolve the problem is that we need to choose a computer C that both computer A and B can access. At the same time, we need to deploy a port forwarding software on computer C. The software will forward request to the VNC server on computer B and forward back response to the VNC client on computer A. This will make the VNC client think it is directly talking with the VNC server. So the software is playing the role of forwarding data here like a router. Of course, you can choose another way to resolve the problem. For example, you can choose to create a VPN here. Comparing with VPN China forwarding software is more easily to be understood and installed.
Another advantage of port forwarding software is that it can turn none SSL software to be more safe by using SSL technology. For example, the communication between VNC client and server is not encrypted. Maybe this is risky. Because the communication data can be easily get by hacker. But we can deploy a port forwarding software with SSL function between the VNC client and server. Then the communication will be encrypted.