In this Microsoft PowerApps tutorial for Responsive design, we will walk through setting up your App for responsiveness along with understanding the App & Screen properties, building responsive galleries & responsive forms.

Responsive Gallery 17:00
Responsive Form Control 22:26

If you create a responsive layout, controls can respond to different devices or window sizes, making various experiences feel more natural. To achieve responsive layout, you adjust some settings and write expressions throughout your app.

Microsoft Blog: https://docs.microsoft.com/en-us/powerapps/maker/canvas-apps/create-responsive-layout