How to make my containers communicate with one another in a Google cloud VM instance?

I have a very simple full-stack TODO app using react-node/express-postgres. I created two images one for react and one for the server using Docker and push them to the Docker Hub. Then I created a VM instance in the google cloud platform using Linux Operating system ubuntu-1804. Downloaded Docker and Postgres in my VM and pull the two images (react, server) from Docker Hub and created two individual container for my images. Now I want to make them talk to each other but I don’t know how, don’t know where to start?
Goal: configure ports to have my simple todo app work in my VM

Thank you for any leads, articles, tutorials

Source: Docker Questions