Why does the screen on my Samsung Galaxy S8 go black during the use of apps?

[Android Central Question]

Why does the screen on my Samsung Galaxy S8 go black in the middle of watching a 60 second video using various apps? This issue has occurred primarily using Instagram and Facebook. I've recently switched to the Samsung Galaxy from an iPhone, this issue never occurred using iPhone. Is there some feature that can be turned on that notifies the device that you are using an app and do not want the screen to shut off?