Having been training regularly for the better part of 5 years, I have formed the opinion that the hip hinge is the single most crucial movement that you should learn how to do properly. It is the mother of all movements. The key to good form. The secret to constantly new PRs.
You get the idea.
And you will never, ever learn proper hip hinge movement if all you do is use the machines at your typical commercial gym. Failure to learn the hip hinge means failure to do deadlifts, squats, kettlebell swings, snatches... a whole plethora of crucial exercises.
Heck, I only learned the existence of my hips only after a year of going to the gym regularly. And surprise, surprise... I didn't learn about the hip hinge movement in the gym. Okay, so how does a proper hip hinge look like?
Most people's forms are like the one on the left. You tend to bend your back instead of pushing your glorious butt out for all the world to see. One of the better coaching ques I've encountered is when the trainer tells the trainee to "push your butt out so that it touches the wall". Just like the lady does in the pic below:
For a better explanation, just watch the video below: