You can consider docker image as a blue print some of already made containers. Consider docker images a drawing or picture of your favourite toy. It contains the details of how your toy looks.
Consider it like a magical box that can hold your favourite toy inside. When you add your image you can use the magical box to create an exact copy of your toy.
It is a snapshot or a blueprint of a complete environment for an application. It includes everything like what the application needs to run such as libraries, dependencies, config etc. It kind of encapsulate the application and all the requirements together.
A container is an actual running instance of the environment configured by the image. When we run a docker image it creates a live and running container. These containers isolated and very lightweight.
A big difference b/w containers and Virtual Machines is that containers share the host Operating System Kernel.
Containers are isolated from each other and from the host OS but they all share the same kernel.