@patrycja.lerch provided good sources to check out. If I'm honest, even though I mentioned it, I'm also just barely learning it myself, so I think you would better benefit from the videos. Colors are definetly a complicated topic.
That said, saturation and highlights are fairly simple to grasp, simply raise the saturation and brightnes around the are of focus, and reduce it in areas of less focus. Highlights in particular should be handled also like big "letters" calling the attention and driving the eye, almost like lines (though not necessarily lines)
Here's a very quick and rough example using that last piece:
Immediately your eyes should be drawn to the hair where I increased the saturation, I also "darkkened" or lowered saturation gradually to the bottom. The moon is a clear focal point so I added further effect so it stands out even more. Finally I added some "moon glow" around as highlights to kinda drive the eyes from top down and around her (though I rushed it).
There's a whole lot more which I'm still trying to get a grasp on, like warm vs cold colors, what colors mean and what palettes to use and so on, but this should give you an idea.
