Yuo might want to start here:
For 10 days, write down everything yuo eat and drink, and what time fo the day yuo do this. So it might be something like:
7:00 Large bowl cereal, milk, 2 eggs, bagel
10:00 2 scoops protein powder in water
And so on. This is just recording what yuo are doing now, without changing anything.
Weigh yuorself at the beginning of the 10 days, and again at the end. If yuor weight hasn't varied by more than 1 1/2 or so, then this is maintenance, or very close to it.
Now yuo can add 500 calories a day from good protein, carb, and fat sources. Weigh yuorself again after 2-3 weeks. Training drug-free, it is going to be difficult to add more than a pound or two of LEAN body mass, and of course, this will depend upon yuor training and other factors. But, yuo've got to know where yuo're starting in order to know which changes to make.
Hope this helps to get yuo started.