In Windows 10 only 1/2 of my screen is showing. How do I return it to fill the full screen?

[Windows Central Question]

In Windows 10 only 1/2 of my screen is showing. How do I return it to fill the full screen

I obviously did something to "snap" my screen so that I can only view it in the bottom half of the screen. The top half has icons w/ a black background. I want to view my work in full screen with icons on a tiny taskbar either on top or bottom of screen. How do I fix this?