The golf swing is fundamentally a rotational movement. From a square and straight set up position, the shoulders will rotate to around 90° in the backswing in order to generate power. This will have the effect of encouraging the hips to turn in the backswing also.
At the top of the backswing, you should notice approximately 45° of hip rotation. Too little hip rotation can result in a backswing that is too short. Too much hip rotation in the backswing can result in a swing that is too long and too inconsistent.
There should be a small feeling of resistance as the hips resist the shoulder turn. It is the build up of this resistance that can produce a powerful uncoiling action at the start of the downswing as the hips move back through their original position towards the target, and finish facing square on to the target, 90° open from the original setup position.
To simplify this entire feeling, focus on the position of your belt buckle. At set up your belt buckle points to the ball, during your backswing your belt buckle points just behind your rear foot in your downswing, and into impact your belt buckle turns to face fully towards your target. This should give you the correct feeling for loading up and releasing with your hips for powerful and consistent golf shots.