Most people use an operating system like Windows, MacOS or Linux. Furthermore, some people have installed runtimes, libraries and databases like Python, NodeJS, Ruby, MySQL, PostgreSQL etc.
Short: We all have very different systems in use.
Problem: It is tedious to setup working environments, that fulfill all needed runtimes and dependencies to run a specific application. Moreover, after working with this specific application, it is tedious to clean up the polluted environment. A lot of orphaned runtimes and dependencies get accumulated.
Solution: Docker saves you the stress by isolating your application and its dependencies into a single self-contained unit that can reliably run anywhere.
Docker Image: A docker image is like a recipe. An image is built from Dockerfile which is a text document that contains instructions on how docker should build an image.
Docker Container: A docker container is a cookie, built from the recipe (docker image). In technical language, a docker container is as an instance of a docker image.
Docker compose: A working software is never an island, it will most likely depend on a bunch of other things like database, cache and even other services. It's best practice to have each of these in their respective container. With docker-compose, you can define a multi-container application in a single file which can be spun up in a single command.
docker images -a: show all images (recipes)docker ps -a: show all containers (cookies built from recipes)docker pull <imagename>: download recipe from docker hubdocker search <searchterm>: search docker hub for searchtermdocker run <imagename>: run image to get a container (run recipe to bake cookie)