I wouldn't worry about Docker (yet) until it solves a problem for you!
As others have mentioned Docker allows you to run your app in a 'container' that is segregated from the rest of the processes running on your computer.
In some cases Docker is used as an alternative to setting up your development environment with all the tools needed to develop an app. You just run the app in Docker and all your dependencies are within this single container.
I use Docker to help manage the Deployments of some of my side projects. This really starts getting into more of the Devops/SRE side of things. If that is stuff you are interested in I think learning about Docker and containers is a great idea!
But if you are wanting to focus more on application development, I wouldn't worry to much about Docker, until you need something to help make it easier to run or deploy your apps!
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