Well first off you need to know how much your body burns or needs in calories per day or find your BMR which is how many calories you burn by doing jack shit.
Go online find a BRM calculator.
Lets say that it says 1500 is your BMR that means you need to eat 1500 a day to stay the same, this is when you are not doing anything besides sitting on your ass that is how much your body will need. If you are actually not doing shit around the house but maybe walking around or going to the store than add maybe like 200 so eat 1700 if you are active that day not super active just walking around the house or something that doesnt require alot of activity.
usually when lifting weights you can burn up to 500 cals
So if your BMR is 1500 on days that you lift weights you burn about 500 calories so you add 500 to 1500 and your body will need 2000 caloires on days you lift TO STAY THE SAME
So if you want to gain or lose weight just add calories, since you want to get bigger add 300-500 caloires on to how many calories you need a day to stay the same, so on days that you dont do crap you may eat 2000 to gain weight and on days you lift you would eat 2500 to gain weight
3500 cals= 1 pounds, so if you eat and extra 500 cals a day that is 500X7 because there are 7 days in a week so 500X7= 3500 extra cals every week so you should look to gain about 1 pound every week, if you are gaining like 2-3 pounds a week than alot of it is fat and not muscle.
so eat 300-500 more than your body burns in cals per day.
drink lots of water like a gallon a day. Water helps burn fat too.
If you need quick calories peanut butter and milk are easy ways to get calories fast.
weight gainers will help if you have a hard time eating enough calories, some weight gainers have 1000 calories in just one scoop so if you took 2 scoops that would be a whole day worth of eating so weight gainers are great and easy to gain weight.
supps that will help you gain weight are really just weight gainers and creatine
creatine will make you gain weight because of the water that is stored in your body so you could gain 5-10 pounds from creatine in just a couple weeks.
Creatine is probably the most effective supplement that actually isnt BS and works quite well. Of course next step up from creatine is roids but guessing that you want to stay natural creatine is going to be the most effective supplement you take.
Creatine mono is the most used and most proven and effective to work. Alot of supps are bs and some arnt.