There are various ways to make & use GIFs in Canva.
First of all, you can simply take any Canva video and reduce the video length and then export it as a GIF.
Secondly, you can also use pre-existing Canva GIFs. These can be found under "Elements." Just search for "Stickers" and you will find lots of different GIFs.
Lastly, you can also upload your own video footage and then make a GIF out of these by simply making sure to export these as GIFs in Canva.
As a small bonus, at the end of this video, I will also show you how to download animated GIFs from Canva and how to remove the background of these GIFS later on in third-party video editing software (removing the background of GIFs can't be done in Canva itself...this is true for both Canva Free and Canva Pro).
