I know how your feeling as I felt the same I spent hours and hours browsing the net for the best and quickest ways to gain weight. When you go to the gym you should be doing big compound exercises i.e deadlifts, bench press, squats etc. Start off with light weights to make sure you get good form and comfortable with the movement range. I workout 4 times a week: legs, chest/tris, back/bis, shoulders/abs. Doing only 8-12 reps spending around 35-40mins (not inc warm up/down) any longer and your body will start eating itself.
As the others have said you need to eat MORE split it up it up to 6 meals a day, if you add an extra 1000 calories a day to what you normally eat you should see a couple lbs gained a week. If you parents don't like the idea of weight gainers try drinking full fat milk, 2 pints is like 650 calories and has good source of protein and vitamins.
The hardest part is being consistent there is no point eating loads one day then nothing the next.I'm not how much your looking to put on but a stone is achievable in like 4-6 weeks? Make sure the food your getting down is good to support muscle growth from the gym. lots of protein and carbs for energy.
I weighed 141lb at the beginning of december I'm now at 158lb and still going. Then I'll start cutting for summer