Many people workout to add and build muscle.
There are principles at play here in achieving this goal, which can be boiled down to:
Exercising to challenge muscles, not simply to work them.
Consuming more protein than is broken down when exercising.
Eating more calories than are burned during a typical day.
Make the above principles central to your workout programme, avoid injury and rest sensibly, and you will indeed grow.
To supplement the above, you may want to consider adding the following into the mix:
Creatine is a molecule that’s produced naturally in the body and which provides energy for muscles and other tissues. Studies suggest that creatine can help increase muscle mass.
To gain muscle, you need to consume more protein than your body breaks down through natural processes. Many people achieve this through their diet (and particularly through increasing what they eat and when). For those not so interested in eating, eating, eating, taking a protein supplement (in the form of a shake, for example), which can help in boosting the amount of protein consumed during a typical day.
Weight gainers are high-calorie products, marketed in a similar way to protein supplements, and are designed to help people consume more calories.
Beta-alanine, an amino acid, reduces fatigue and may increase exercise performance. There is also a certain amount of evidence that suggests it can help increase muscle mass.
Branched-chain amino acids (BCAAs) consist of leucine, isoleucine and valine and are important for muscle growth. They are found in many foods (though may not be required as a supplement for most people).
Beta-hydroxy beta-methyl butyrate (HMB) is a molecule which is produced when the body processes leucine, an amino acid. As a booster, HMB might help increase muscle mass in those starting a muscle-building programme.
So, there you have it - a short primer on supplements.
But remember, to build muscle, you need to consume enough calories and protein and also exercise effectively (especially resistance and weight training). If you want to add to the above mix, or need to have a quick start (and have the resources to do so), you may find that supplements might help.