Hey buddy! It's good to hear that you started gym. It's one step to gaining mass although it's kinda hypocrite of me to say that since I stopped going to gym for some time. Anyways, I think I have sorta the same problem as you cause since I was around form 4 or so.. I have retained my weight at around 60-65 kg. Now it is around 63-64 kg and I'm around 177cm.

In growing, it varies for each person as the energy spent daily is different. It depends on your lifestyle. For me, I have a very sporty lifestyle so I spent more energy. It also depends on your metabolism rate. How fast your body turns food into energy.

Basically, based on my experince, to gain weight, get exercising and eat a lot! I'm not sure about your metabolism rate but for me, since I have a high metabolism rate, I seldom worry about the fats (you won't wanna have a big belly). If you have a slower metabolism rate, get some exercise to burn the fats or watch your fat intake.

Another thing, (although I'm not very sure with this, I heard it somewhere..) eat slow-acting carbs at night before bed. The person said that this will provide the food for your stomach to digest cause during sleep there are still juices flowing in your stomach and if you don't let it digest something, it will burn some of your mass. Not really sure about this but it was what I was told.

As for gym and the "when I press the muscle, it's a bit hard compared to the right forearm" thingy, that's just you feeling the pump. When you're doing gym and you hit hard on your muscle, blood flow will increase in that area (there are more scientific way of explaining it but I guess you can just google it ) making it harder. It's a good feeling by the way and it means you're working that muscle well. The reason why you feel more pump on your left is maybe because your right arm is stronger so I'm probably guessing that you're a righty?

By the way, I hope this helps and if anything I said was incorrect, do tell me. You can't be correct all the time Cheers buddy and I wish you all the best. Going to hit the gym hard soon to myself.

It depends. Usually people tend to complete an exercise first before moving on,, but you can superset it. Meaning two exercise, no rest in between. Example, Bicep curl 15 reps, and then straight to tricep extension 15 reps. Then 30-60 seconds rest before doing it again.