Being apprehensive about a smartphone is understandable, the industry just keeps packing more and more functionality into them every production cycle.
Before you do get into installing things on your own, get comfortable using your phone as is. Sit down and just start going through the Settings menu. That's your link to managing the different aspects of your particular phone. (Every different phone model has its own hardware configuration inside, and the Settings menu will reflect that, along with all the different features that vary between the different versions of Android.)
Open up the Settings menu and just start at the top and eventually work your way down the list one by one. A lot of those items will have their own sub-menus, and even some of those will have their own sub-menus so don't be surprised by the complexity that some things might appear to be. They're typically contextual so they need to nested within each other, and be aware some sub-menu options are accessed by tapping on a wrench icon or a three dot icon in the top menubar. Also, you'll encounter a lot of what appear to be odd phrasing and terminology. Some will be Android-based, some more specific to Samsung (Samsung is notorious for heavily branding its own products) so just do an online search for explanations and definitions. There's plenty of info online for Android and for Samsung so it's actually a problem now with the over-abundance of resulting links when doing a search these days.
Anyway, once you get more comfortable and familiar with all the things your S7 Edge can do, it shouldn't feel so daunting to change things around to make it more suitable to your needs. And don't rush things, we all learn at a different pace.
