How do you throw a punch?

Ive been told to twist my foot like squashing a bug and NOTHING!

My leg kinda spins, and theres no power, my hips dont rotate, and theres no transfer of weight from one foot to another.

Its like the only instruction you get is twist the foot and then somehow you are magically expected to be able to throw a boxing punch!

Well I cant and it sucks!

(A boxing punch)

I will assume you're starting off with a right cross. There are cues but the only real way to learn is to be taught and with lots of practice. You should have balance as you're twisting your foot your heel should be off the ground, your hip should follow your twist and if you remember to jack your left shoulder back pretty fast your weight should transfer from your right foot to your left. It's really hard to get my point across without showing you in person so I suggest you hit YouTube up and ask for right cross, hook and uppercut instructional and practice on a bag. Break it down, once it feels right on the bag you will know.

Start with teaching the person how to breathe.

Then how to stand.
Then a structured stance from feet placement to knees to bladed body frame to elbows in and hands high and chin down.
Then how to feel the ground when they throw a jab and cross.

The rest will be easier....

Use focus gloves, left hand to left glove, right hand to right glove.

Do what all these guys said but in addition all these tips must be done with timing. Here is where you get faster and hit harder. Coordinating all these aspects in unified time makes everything work. Some people feel/hear this time naturally some have no clue to what I am talking about.

Example stand a little more then an arms length away from a heavy bag, or your buddies face...:-)
Either lead, match it with same lead arm and punch as fast as you can, (The jab). Hit just hard enough to hear a nice solid pop. Give yourself a starting cue , as soon as you blink throw the punch. Do it roughly 50 times or until you hear/feel the distance and the time it takes from when you blink to the sound of the bag's pop. The goal is to shorten the time it takes from the blink to the pop. ( you can even use a round timer).

To get faster you have to hear/feel where that shorter time is. If you can't hear/feel it you can't improve on it. To accomplish this step half way closer to the bag and repeat the earlier process. You should now hear the bag pop in half the time meaning you are twice as fast because you are closer by ½. the distance.
The math works. Speed will give you power when the mechanics are right and in time with each other. Many people don't know what time is, how to break it down or how to work with it.