Protein shakes usually have a bad reputation, usually associated with people with too many muscles that are often not well seen. But it's not just a special product for people who follow a diet to achieve a goal, or for those who spend long hours in the gym.
Protein is essential for life, all the structures in your body are built, at least in part, from protein. Literally your whole body is protein and fat.
If you are signed up for the gym and normally do weight training you will have to work hard to build muscle. Protein shake can help you maximize this effort. Intense training leads to muscle damage and much of the optimization of your weight training results requires basic elements to rebuild the muscle, so you need protein.
Protein is known to have a satiating effect on the diet, helping you feel fuller for longer than carbohydrates and fats. Protein also has a thermal effect, which means it helps the body spend more energy to digest carbohydrates or fats. This is what has made protein intake associated with weight loss and especially fat loss.