re: SSK
SSK (https://roaminggamer.github.io/RGDocs/pages/SSK2/) is my own free library of solutions for common dev problems.
It has been around for about 6 years here (and comes from my original SSK library for Torque).
It is not perfect, but it is pretty solid. Peruse the docs to see some of what it offers.
I never code w/o it.
re: The Video
You’re going to learn how to do basic vector math to accomplish that kind of behavior. Aiming, firing, facing, …
You’re also going to have to implement some kind of path finding code (try jumper) to allow units to walk around complex area, objects, and avoid each other.
You’ll need to learn how to code up camera code and understand how to drag the world or select a position from a mini-map and have that choose the camera focus/center.
There is a bunch of interface work there too.
Then of course, you’ll need to learn how to give metrics to units and probably some basic state-machines to govern their behavior.
There is, much, much, …, more, but that was at first glance.