Task: I want to add slide 3 and add the video AP.mp4 to the slide 3 in the Microsoft PowerPoint app.
Steps:
Go the Edit section
Click on the three dots button at the top right corner of the screen
Click on the New Slide
Click on the A icon at the top of the screen
Click on the Home
Click on the Insert option
Click on the Videos 
Click on the Video
Click on the Recent video