Here is how you create a Voiceover using PowerPoint for PC Users:

1. With your presentation open, on the Slide Show tab, click Record Slide Show.

o Clicking the upper half of the button starts you on the current slide.

o Clicking the lower half of the button gives you the option to start from the beginning or from the current slide.

(The Clear command deletes narrations or timings, so be careful when you use it. Clear is grayed out unless you have previously recorded some slides.)

2. In the Record Slide Show box, check or clear the boxes for your recording, and click Start Recording.

More about these options:

o Slide and animation timings: PowerPoint automatically records the time you spend on each slide, including any animation steps that occur, and the use of any triggers on each slide.

o Narrations, ink, and laser pointer: Record your voice as you run through your presentation. If you use the pen, highlighter, eraser, or laser pointer, PowerPoint records those for playback as well.

Important:   Pen, highlighter, and eraser recording are available only if you have the February 16, 2015 update for PowerPoint 2013 or a later version of PowerPoint installed. In earlier versions of PowerPoint, pen and highlighter strokes are saved as ink annotation shapes.

3. At the top left corner of the window is the Recording toolbar, which you can use to:

o Go to the next slide: 

o Pause the recording: 

o Re-record the current slide: 

If you re-record your narration (including audio, ink, and laser pointer), PowerPoint erases your previously recorded narration (including audio, ink, and laser pointer) when you start recording again on the same slide.

You can also re-record by going to Slide Show > Record Slide Show.

4. To use ink, eraser, or the laser pointer in your recording, right-click the slide, click Pointer options, and pick your tool:

o Laser Pointer

o Pen

o Highlighter

o Eraser (This option is grayed out unless you have previously added ink to some slides.)

To change the color of the ink, click Ink Color.

5. To end your recording, right-click the final slide, and click End Show.

Tip:   When you finish recording your narration, a sound icon appears in the lower-right corner of each slide that has narration.

The recorded slide show timings are automatically saved. Timings are shown in Slide Sorter view just beneath each slide.

In this process, what you record is embedded in each slide, and the recording can be played back in Slide Show. A video file is not created by this recording process. However, if you want a video file, you can save your presentation as a video with a few extra steps.

Preview the recorded slide show

On the Slide Show tab, click From Beginning or From Current Slide.

During playback, your animations, inking actions, laser pointer, audio and video play in sync.

Preview the recorded audio

In Normal view, click the sound icon in the lower-right corner of the slide, and then click Play.

Here is how you create a Voiceover using PowerPoint for MAC Users:

Record audio and add it to a slide

1. In the navigation pane, click the slide that you want to add sound to.

2. On the Insert menu, point to Audio, and then select Record Audio.

The Record Sound dialog box opens.

3. To start recording, click Record.

4. When you are finished, click Stop.

5. To listen to the sound that you just recorded, click Play.