Start seated with dumbbells in your hands, bend the elbows at 90 degrees, engage your core & push the right side dumbbell & lower, then the left side, then finish with both at the same time. that is one full rep!

Beginner: 5-7lb dumbbells

Intermediate: 10-15lb dumbbells 

Advanced: 20-35+lb dumbbells

*Modification: You can also use a shoulder press machine or a fixed barbell