Explanation
Box 1: Display Rule
When configuring ribbon elements, you can define specific rules to control when the ribbon elements will display.
Box 2: Action
Define the actions to be performed by a command bar or ribbon control in a <CommandDefinition> element together with rules that control whether the control is enabled or visible in the ribbon.
Box 3: Enable Rule
When configuring ribbon elements, you can define specific rules to control when the ribbon elements are enabled.
Reference:
https://docs.microsoft.com/en-us/powerapps/developer/model-driven-apps/define-ribbon-enable-rules
https://docs.microsoft.com/en-us/powerapps/developer/model-driven-apps/define-ribbon-display-rules
https://docs.microsoft.com/en-us/powerapps/developer/model-driven-apps/define-ribbon-display-rules
https://docs.microsoft.com/en-us/powerapps/developer/model-driven-apps/define-ribbon-actions
https://docs.microsoft.com/en-us/powerapps/developer/model-driven-apps/define-ribbon-actions