Focus When Multiple Windows Are Open

I'm relatively new to the Mac world (purchased mine just a couple months ago). Can you tell me...when I have two windows open of the same app (i.e. 2 Firefox windows) and they are on top of each other, how can I switch to the one in the back. I realize I can do the "4-finger swipedown" to see all open windows and select it from there, but I'm wondering if there is any other way.
I'm asking because I have been on Windows my entire life until now and every window always displays in the task bar at the bottom of the screen, but Mac does not appear to work this way.