The shoulder press, also known as the overhead press, is one of the best exercises for your upper body. There are many different shoulder press machines, but they all do the same job - lifting a heavy weight over your head.
This exercise will build you wider and bigger shoulders, And since its a compound movement, it will also work the traps, triceps, serratus and upper chest.
The shoulder press can be done with a machine, or with free weights like barbell or dumbbells. It is generally more recommended to use free weights, because the weights require much more muscles to stabilize the movement, giving you a more effective and functional movement. While the machine neglects these muscles which might cause strength imbalances increasing your risk of injury.
Yet, There are some benefits using a machine. If you don't have the proper form the machine will force your body in the right form for the exercise. Using the machine is simpler, faster and usually more fun, so it might fit better for beginners, and it allows you to easily progress the weight as you're getting stronger. The machine version is also easier on the joints, so it is a good choice if you're unable to do free weights shoulder presses due to injury or pain.
Don't flare your elbows to the sides. Flaring the elbows to the sides puts you in mechanical disadvantage, and it is unnatural movement for the shoulder joint that might lead to injury. Align your arms in slight angle towards the front.
Keep your back straight and pushed firmly against the back support pad. Make sure to have a natural arch in your lower back.
Don't lower the handles completely down, Lower them a slightly less so that the tension will stay on your muscles the whole time.