It is perform standing ,holding and lifting the barbell up and down consecutively, you will need a straight bar for this exercise.
The down motion should be slightly slower than the up motion, be concentrate and focus on pushing yourself up and lowering down. Repeat the process again to your desired reps.
It is advised to use a weighted barbell for a barbell behind the neck shoulder press is mostly accomplished with a weighted barbell.
This particular exercise also help to train the anterior, lateral deltoid it also helps in training the pectoral and serratus at the sometime with just only this exercise you can do more.