What is Docker?
Docker is a containerization platform that packages your app and all its dependencies together in the form called a docker container to ensure that your application works seamlessly in any environment. This environment might be a production or staging server.

Imagine we already have an application running PHP 5.3 on a server and want to deploy a new application which requires PHP 7.2 on that same server. This will cause some version conflict on that server and also might cause some features in the existing application to fail3

What is a Docker Container

Think of a Docker container as above image. There are multiple applications running on the same machine. These applications are put into docker containers and any changes made on these containers does not affect the other container. Each container has different Os running on the same physical machine. Docker helps you to create, deploy and run applications using containers.