Dockware has different images.
It's very easy to decide what you need once you know the basics.
Here are some short key facts about the different images.
Use this if you do not need to develop or build anything. Playing around with Shopware, testing your plugins or research for your concepts. No PSH file included.
This image offers a full stack for building artefacts, running debuggers and more. It comes with a preinstalled Shopware 6 version. Great if you want to develop plugins and check them out in different Shopware versions or want to easily switch Shopware versions using the image tags. If you want to organize and manage the Shopware version on your own, and have everything under your control in a more persistent way, you might want to use ESSENTIALS. No PSH file included.
This is a prepared GIT setup of Shopware 6 from Github. It comes with the commit where it has been last built. The benefit is a good start with a prepared GIT repository infrastructure to develop Shopware 6. Comes with PSH file.
This image comes without Shopware. It's great if you run your own full projects, such as projects for clients or your own shop. Essentials is perfect environment for your Shopware shop with all required services as LAMP container. You can download and install any Shopware version easy with the provided make command. Mount your DocRoot + MySQL and you can individually maintain, update and change your shop project.
This is a perfect fit for anything not related to Shopware. A simple PHP application, full Symfony App or anything else (Shopware would also work). It comes without any additional services and is a great and slim environment to code.