Start by going to your Settings Menu by clicking the little down arrow/triangle at the top of the screen, then click on Settings.
On the bar on the left side of the screen, at the bottom find Videos and click on that.
You’ll see two sections, one about default quality, and one that says Auto-Play Videos. If you do not want to have the videos auto play, click the arrow by On and turn it to Off.
In this same area, you can click for instructions to turn Auto Play off on your mobile devices, or follow our directions in the articles linked above.