During nights 1+2 you don't need to use the flashlight much because you can see Withered Poundinger Shell and Miss Shella's eyes at the door. You only need the flashlight to wind up the music box.

After each night you need to collect evidence of the animatronics, obvs. If you see any animatronics take a picture immediately and wait for him/her to move on. But if you here breathing don't use the flashlight.

During night 3 Withered Ket is active. You need to flash him several times to make him go away. But the other animatronics aren't active when Ket's active. (The music box still winds down though...)

That's all of chapter 1.

I hope this helps.