Most people buy into the commercials that say that gain mass muscle can be achieved by doing nothing when you consume their product.
That is not true one single bit, there are products that work and help you, but each one of them requires that you constantly workout.
Otherwise you will gain weight; you will not gain mass muscle.
What you need is to gain mass muscle with top notch workout.
Like any other workout you need to start with stretching your body and your muscles, you don't want an injury or a strain muscle.
Warm up is often skipped, and that is one of the basic mistakes, a top notch workout needs to have a good stretching to begin with.
After the stretching comes the gain mass muscle top notch workout:

• Do 3 to 5 easy series with small weights to warm your muscles a bit
• Go from the upper body to your legs
• Do full body workout, don't concentrate on one part only and don't neglect the others
• Do heavier weights to the maximum, no more than 10 repetitions, also 3 to 5 sets per exercise
• Eat healthy food full of protein, sleep and rest and then repeat

It's not hard to gain muscles; it's not hard at all.
But to do so you need to have discipline and you need to push yourself sometimes.
Remember that nothing can be achieved if you don't try, and with this gain mass muscle routine you will see results very fast, so don't waste your time thinking about it, just try it.