If I say "hip hinge", it will likely mean little to nothing.
However It is an important movement that is done as part of a lot of exercises such as hip thrusts, cable pull throughs, kettlebell swings, and romanian deadlifts.
It is fairly technical, requires coordination and getting it right takes practice.
I've put a video together showing how to build the movement up from scratch.
If you give this a try and struggle, drop me a message and I'll be happy to help!
This is my, mostly, Personal Trainer musings and information which I hope you'll find helpful!