A major new feature in iPadOS 15 is a revamped multitasking. A multitasking menu will appear at the top of apps and allows you to start Split View or Slide Over With just a tap.
The new shelf will allow you to view all open windows for an app, like Safari or Pages. You can quickly switch between different windows and add or close a window.
Split View spaces can be created on a single screen with the App Switcher. You can create a Split View by dragging one app over another.
Keyboard users can create a shortcut for switching between Split View and Slide Over.