You can record a narration on your PowerPoint Slides and save them as as PowerPoint slides and also export them as a movie file.
Also strongly consider adding captioning to your PowerPoint recording. See how.
A. You can record a narration on your PowerPoint Slides in two ways.
Method 1: Insert audio, video in each slide
Method 2: Record your presentation from the Slide Show
B. In both cases, you can redo your recording on all, or selected slides.
C. To export it as a movie, go to File > Export > and select the file format (MP4 in most cases).