Freddy: He will start to search for you when you are in the dark, he doesn't like light. Turning the flashlight ON will make him less agitaded.

Bonnie: He has good vision, if he spots you, he will alert Chica of your location, and turn your flashlight ON so she can see you.

Chica: She will chase you if you're seen, just like Bonnie, she can't see you in the dark, but you can still crouch behind objects in the light and not get seen.

It is really hard when you're in the start, but it gets super easy when you understand the mechanics. Just like the PS1 games, there is not many tutorials or tips in the game