An "action button" is a clickable or touchable element on a device or webpage that performs a specific action when activated. It is usually labeled with a word or an icon to indicate the action it will take.
When you've got everything set up to your liking, head to the app's main menu and tap the floating action button on the left side of the screen. (android.gadgethacks.com)
From here, tap the floating action button in the bottom - right corner, then select some apps that you would like to use this feature with. (android.gadgethacks.com)
You can customize the order of quick action buttons and select the apps you want to access often. (thewindowsclub.com)