How to push press
As mentioned in the video, the key thing here is to use the explosive action of the legs to shift the weight above the head. It is important that the bar finishes above the crown of the head. You may get away with it if the bar finishes slightly behind the head but you are asking for shoulder injury if you press in front of the head.
When doing the push press, ensure that you lock your arms in the top position to allow your body to support the load. When bringing the bar back down, allow the bar to rest across the shoulders keeping your elbows ‘pinched’ upwards and inwards. This is the same position as the front squat.