Originally Posted by
PFerrari
Dastardly isn't explain it overly well. Basically a push press you have you have your knees locked before your arms lock out. You are not allow to rebend the knees after you do your dip and drive. A push jerk you "catch" the bar it's your knees bent. So you dip and drive and then rebend your knees and use your arms to push the bar up as well as push your body under the bar.
If you've only been pressing, you'll have a better chance at making a push press in the beginning. A push jerk requires a lot of timing, technique, flexibility, and there is less room for error than with a push press.