Can anyone help me how to create dockerfile or docker-compose file

I have public ip for example: - x.x.x.x and i have created 2 docker containers one with piehole and another with openvpn.
How to connect each other and i created client from openvpn so that i can use that openvn file to get into that network.
How to connect openvpn docker to piehole docker can anyone help me?
How to create port forwarding from one docker to another is there any commands?