FYI: GIF stands for Graphic Interchange Format. It's a computer file format for graphic images. Animated gifs are graphic images that move, not "videos". For instructions on adding a video file to PowerPoint, see these instructions.
To add an animated GIF to a presentation:
1. Search online for the appropriate GIF file that you are seeking.
2. Save the GIF to your computer.
3. Open PowerPoint.
4. On the Slides tab in Normal view, click the slide in which you want to embed an animated GIF file.
5. Click on the Insert tab.
6. Click on Picture.
7. Browse your computer to find the GIF that you had previously saved.
8. Click Insert.
9. Adjust size of your video if necessary by grabbing the corners of the video
and stretch to desired size.
10. Click on Slide Show tab, click Start from Beginning or Start from Current Slide to preview.