Windows 10: Windows Snap Feature

I created a permanent snap box in one corner of my monitor screen. It was defined by a yellow border that would appear when I moved a window into the box. The window would automatically resize to fit the box. I just got a new computer and can't remember how to create that box. I've read all about the snap feature in Windows 10, but I haven't seen any information on how to do it. It's a very useful feature. It can't be that hard to set up. What am I missing?

:)