Exercises can be split into two categories. Isolation exercises and compound exercises. As the name suggests isolation exercises only work one particular muscle. Compound exercises on the other hand work out multiple muscles at once. Bench pressing is one of those compound exercises. It engages the chest, triceps, shoulders and arms all at once. This is why it is an effective exercise both to build muscle and to lose weight.
The bench press is done lying flat on a bench and pushing a bar loaded with weights away from your chest. It can be done in several ways and many people have differing opinions on which way is the most effective. Some people push the bar up and down slowly. Others think a more explosive movement is more beneficial. There is no definitive proof one way is better than the other.
When doing the bench press, it is important to keep your shoulders back and flat against the bench. This will ensure you are putting the majority of the load on your chest muscles and not your arms. This will also ensure you will not injure your back. Many people arch their back very high when benching. While this does help you lift more weight, there is a much higher chance of injury.
Compound exercises like the bench press are the best kind of exercises for those that are just starting out. It encourages weight loss and helps but on more muscle mass in a shorter period of time. Isolation exercises can be done to compliment an already conditioned physique.