Key to diet is balance. Google food pyramid to get volume balance only, not portion numbers. Mostly complex carb (starchy) foods, they are not the devil, with plenty of veg and fruit, sensible meat and dairy and only the slightest trace of additives and treats, this includes sauces in food.
If you want to gain weight eat more of a well balanced diet, not majoring on any one area unless the body is crying out for it, ignore the sensation if this is for sugar or fried food.
If you are eating more food than you are burnign you will gain weight. Whether that weight is all fat or some muscle and some fat will come down to training or lack thereof.
I am automatically mis-trusting of quick fix programs, and with good reason, most are rubbish. Check yours out fully and use the simple system if in doubt, don't.
Training takes time to achieve results, as does diet. If you want results in a month, go to a surgeon for implants, if you want real muscle and fitness be ready for the ride of a lifetime and to spend a life time doing it.
I was a little older than you when I started weights as an adult and like many started in late spring. Unlike many wanting a good body for the summer I was thinking of the next years summer, and that is why I succeeded where many failed. Fast forward a few years, I am now a functional trainer who has no interest in aesthetic but I still get people saying they want to look more like me, must be the balding greying wrinkly effect they are after.