Apple's iOS 14 has a lot of new features and many of them geared toward customizing and simplifying the Home Screen. Chief among those additions is the ability to create widgets that help pin certain apps and functionality to the Home Screen without necessarily having to open said apps manually.
After choosing the style you want, you can tap "selected photo" at the bottom of the app interface and then tap "choose photo" beneath the widget icon which will allow you to load in photos from your camera roll. Choose the desired photo and navigate back by tapping the "small" icon at the top left corner of the screen.
Here you'll want to tap the top center icon of the screen where it says "tap to rename" choose your widget name (i.e. if you're making this a FFVII themed Home Screen like me, you could choose "materia" or something to that effect). Tap "save" in the right corner of the screen and concrete your newly created photo widget in the app.