To do this - open Google Slides and slide your cursor over to the word "INSERT" when you slide down you will see the word VIDEO with a video icon. Click on that and a page will open up that looks like this -
From here type in either the specific name of the video or category that you would like -
"Bill Nye Science Guy" or "Bill Nye Science Guy - Physics" for example
and it will bring you to a few selections on the Internet. You can then click on the specific one that you'd like and insert it onto your slide where it will now be able to play once you activate it from your Google Presentation!