Step1: Double-tap the slide that you want to comment on.
Step2: Tap the New Comment button on the floating toolbar.
Step3: The floating toolbar in PowerPoint for Android has a New Comment command
Step4: The Comments pane appears full screen with a blank notation indicating your name and the date.
Step5: Type your comment. Press Done to resize the Comments pane and make your slide visible again.
Step6: You can use the toolbar to navigate backward and forward through comments.