& one more thing, told by a friend, if one work outs well with taking powder regularly & later, if he stops working out, all body parts [biceps etc] become saggy ? Is it true or myth ?
Taking powder has no effect on being 'saggy' later or not. It just adds fuel to to your diet, a.k.a. it supplements the food you eat. And moreover, if your main food intake is improper, then it doesn't make much sense to take supplement in the first place.
When you go to a gym, you hear a thousand facts. Some of them coming from guys who look well built and are really fit. But only 10% of those facts are actually true, rest are all myths.
It would be wise to follow a proper workout, with a goal to do it with perfect *form* first, and later worry about adding weights and reps. Out of gym, follow a proper diet --> Lots of proteins, decent amount of carbs, less of fats. Though you can vary the diet based on your goals, I was just giving a basic idea.