Leg drive is the source of confusion for many lifters. A lot of lifters know what it is, but struggle with how to do it.
I know, I had trouble with it for a long time.
Like a lot of lifters, I made the mistake of driving my heels straight through the floor, causing my legs to tighten, but my butt to pop right off the bench.
It took me a while, but I realized I had to find the right foot placement and drive my feet forward, like I was trying to poke holes through my shoes with my toes.