In iPadOS, you can drag and drop files between apps just as you would on your desktop or laptop computer. This works with just about any kind of file, provided the relevant app has been updated to support the feature. All of the default iPadOS apps are compatible, as are many more third-party apps.
The easiest way to get the most of drag and drop is to try it with two apps open simultaneously in Split View. (Reminder: to do this, swipe up from the bottom of the screen to bring up the app dock, then press and drag an app icon onto the main view. Now both apps will be running at once.)
Now just locate, touch and hold the first file you want to exchange, then drag from one app to the other. It’s particularly useful for moving images around. Try dragging a picture from Photos to Notes or from Safari to Mail.