When you want to create a video to be viewed on a specific screen size, you need to know your ratios, man. Ratios, in this case, are not when someone on social media gets “owned” by savage comments a la internet trolls, but instead is the relationship of screen height-to-width. Knowing your ratios ensures that you show the right-sized video for the right screen.
This is like math, man. Length times width for the screen-size people will view it on. Back in different times, 4×3 was all the rage, now it takes 16×9 to get everything sized appropriately for the screen.