My Advice For New Trainees

My advice for now is eat as much as you can and train as hard as you can. You already know that you already aren't eating enough if you aren't gaining weight and you also probably aren't training hard enough. 

You probably can't even train hard enough yet because you don't know how!
Functionally if you're a new trainee then you probably aren't practised in exerting yourself, so just try harder every single time you train and practice trying harder.

Fully exerting yourself in the gym will also increase your appetite which is obviously useful if you aren't gaining weight. In my opinion its easier to develop a larger appetite from vigorous training than from counting calories.