The chest is made up of two muscles that work together to make the chest function. The muscle are the pectoralis major and pectoralis minor. Basically, the pectoralis minor is located directly underneath the pectoralis major. Overall, these chest muscles start at the clavicle and insert at the sternum and the armpit area (humerous).
The three different functions of the chest muscles are the side arm pitching motion, the ability to bring your arm up and down at your sides, and the classic arm wresting motion. The basic recommended exercises for building up your chest include the bench press and flyes.
Chest Building Pointers
Though the chest is made up of one single mass of muscle, it should be trained like it was broken into 3 parts. The upper, middle and lower portions of the chest are stimulated best from changing the angle in which you execute the exercise.
The upper chest is best stimulated from exercises done on a 30-45% incline bench. For example incline barbell and dumbbell bench press or incline dumbbell flyes are great upper chest exercises.
The middle chest is best stimulated from exercises done on a flat bench. For example: flat barbell and dumbbell bench press or flat dumbbell flyes are great middle chest exercises.
The lower chest is best stimulated from exercises done on a 30-45% decline bench. For example: decline barbell and dumbbell bench press or decline dumbbell flyes are great lower chest exercises.
I find all areas of the chests respond best in the beginning to low (4-6) or moderate (8-12) rep ranges. Rarely, I will include higher rep ranges for beginners. I believe the heavier weight helps build a more solid foundation that beginners need. I also find that free weights should be your entire focus in the beginning, especially if chest is a weak point for you. The free weights just develop the chest a lot better than machines do, in my opinion.