Push press

Start with a barbell in the front rack position, resting across your front shoulders with your elbows high. Stand with your feet about hip-width apart and your core braced.
Perform a quick, shallow dip by bending at your knees and ankles while keeping your torso upright.
Immediately and explosively drive up with your legs. As the barbell is propelled upward from your shoulders, use your arms to press the weight overhead until your elbows are fully locked out.
Lower the bar with control back to the front rack position to complete the rep.

Tips

Keep your torso upright during the dip by bending at the knees and ankles rather than hinging forward at the hips, so the leg drive transfers directly into the bar.
Time the press so your arms begin pushing the bar overhead as soon as the leg drive launches it off your shoulders, using the upward momentum rather than waiting for it to stall.
Lower the bar back to the front rack position with control rather than dropping it, so you are set up and stable for the next rep.

Dipping too deep or too slowly turns the movement into a slow squat rather than a quick elastic drive, and the leg momentum needed to propel the bar is lost before the press begins.
Letting the elbows drop in the front rack position causes the bar to roll forward off the shoulders before the drive begins.
Pressing the bar forward in an arc rather than straight overhead means the bar finishes in front of the body instead of stacked over the shoulders and hips.