Open PowerPoint and create or open your presentation
Go to the slide where you want to add voice over
Click the Insert tab
Select Audio
Choose Record Audio
Give the recording a name
Click the red Record button
Speak clearly into your microphone
Click Stop when finished
Click OK to insert the audio
Repeat for each slide that needs narration
Adjust the audio icon position if needed
Select the audio icon
Open the Playback tab
Set Start to Automatically if desired
Check Hide During Show if desired
Use Trim Audio if needed
Use Fade In and Fade Out if needed
Save the presentation
Go to Slide Show mode to test the voice over
Check that audio plays correctly on each slide
Export or present the file when ready