Adding a Sound Recording Button to Your PowerPoint Window
You know that PowerPoint, like the other Office programs (e.g., Word, Outlook), has lots of buttons at the top of its window:

You may also know that PowerPoint can open a sound recorder..

that records your voice...

and includes it in your slides.

But! You can also create a button that enables you to do this in one click!
Step 1: Right click on your toolbar and select "customize"

Step 2: Click on "Commands" tab at the top, then click on "Insert" on the left, and find "Record Sound" on the right:

Step 3: Drag that "Record Sound" item to where you want it on your toolbar:

That's it! Close your "Customize" window and now you and your students can record yourselves for your PowerPoint presentations.