Starting the gym, 18M?

18M, 182cm, 65kg.

I've decided I'm finally going to join a gym, but I'm starting from absolute zero. I've never been to a gym before, never followed a workout programme, never tracked calories or protein, don't know what apps to use etc and don't really know where to begin. My main goal is to build muscle and put on size. I'm pretty skinny and don't really have much muscle at the moment.