How do I turn off the feature that shows all the windows at once?

I'm new to El Capitan/Sierra. Often when I'm working, I seem to do something that causes the window I'm in to suddenly minimize so that I can see all open windows at once on the Desktop (all minimized). I don't need this feature, but I don't know what it's called or where it's located in System Preferences, and it's driving me a little nuts. How can I turn it off until such time as I decide I need something like it, if ever? Thanks!