Have a quick look at some of the videos, linked on the top bar above. Maybe the Sara Wager ones, there are a few "How to" videos.... That's possibly the easiest way.

I tried watching a few of them, but every video seems to assume I have any idea what a "calibration frame" is. I also don't understand what a light frame is vs a dark frame vs a flat frame?

Again, I just have a group of pictures of the general sky from my backyard that I'm trying to align properly.

I think it will be very good to have an understanding of those first, here's a random post I found with answers explaining it as well: https://stargazerslounge.com/topic/252760-lights-darks-flats-bias/

APP itself is a rather advanced package to take this kind of data and correct for all the different issues there may be in the photo's you took and to carefully and correctly make them work together. You need proper workflows to create those calibration data properly.