The chest muscle groups:

The pectoralis major

This includes the upper part of the chest from the shoulder to the breastbone. This muscle keeps your arm attached to your drunk, moves your shoulder joint, and rotated and adducts your humerus - the long bone in the upper arm.

The pectoralis minor

As the name might suggest, this is a much smaller muscle which is located just under the pectoralis major. It is responsible for pulling the superior part of your scapula (shoulder bone) and depressing your shoulder point.

The serratus anterior

This muscle covers the first to eight ribs of each side of the chest and the anterior length of the shoulder bone. It pulls your scapula around your thorax to enable you to tilt your arms further forward. It also allows you to pull your scapula forward towards your rib cage and rotate it upwards (such as when you're performing a military press or shoulder press.
The best exercises for building your chest:

The bench press

One of the ‘big three’ compound movements (along with squats and deadlifts), the bench press is arguably the best chest exercise for building overall mass and strength. For the barbell version, simply lie on a bench, arch your back slightly, keep your feet firmly on the floor, then lift the bar, straighten your arms and move the bar down until it touches your chest. Start by lifting enough weight so you can complete the exercises for 6 to 8 reps – and make sure the bar is aligned with your nipples.

You can also do the bench press with dumbbells if you prefer. The same rules apply, although you’ll probably find you can lift less total weight than the barbell version.

Pec deck

Although you'll often notice the pec deck machine is never in use, it is a great exercise for finishing a chest workout. Also targeting your whole chest, the machine gives you extra stability to relieve pressure on your shoulders and help you isolate the movement to minimise triceps involvement.

Sit on the machine, making sure your upper arms are parallel to the floor and that your hand position on the handles is roughly parallel to your nipples. Push the handles together and feel the squeeze in your chest while breathing out. Contract for a second or two, then return to the starting position and repeat. It's a good idea to start with a lower weight and gradually increase as you become stronger over time. Too much weight can put more pressure on your shoulders and increase the risk of injuries.

Alternative: Dumbbell flyes

One of the best chest exercises to follow the bench press, dumbbell flyes also work the entire chest, particularly the fibres near your sternum. Unlike the bench press, it doesn't put much stress on the tricep muscles, so it's a good alternative if your arms are a little sore from a previous workout.