The Barbell Overhead Press works your anterior deltoids, pectorals, triceps and trapezius muscles, in addition to your core, specifically the obliques, transverse abdominis, lower back and spine stabilisers.
To set up, take your hands just wider than shoulder width apart and bring the bar onto your front so that it is resting against your chest and held by your arm with your palms facing forwards, or slightly towards the ceiling. Take a step forwards and stand with your feet shoulder width apart and a slight bend in the knee. From here, press the bar up above your head, reaching the top position when your arms are fully straightened above your head.
Aim to bring the bar all the way back into your chest between each repetition. You should also aim to minimise movement in the rest of your body and your head. Engaging thorough your core will help you do this and maintain balance.