The iPad Dock is a handy area where frequently used apps or apps that you have recently saved can be stored, so you don't have to search through multiple screens or folders to find a specific app. You can also use it to make multitasking easier by opening two or more apps in Slide Over or Split View mode.
First introduced with iOS 11, the Dock gets a few new tricks in iPadOS. The process for adding and rearranging icons is different. And now you can paint the Dock with a dark background by turning on the dark mode. Here you can read how to use the Dock on your iPad.