From complexity comes simplicity...sometimesThere's a lot of good stuff here. Perhaps too much.
While pumping, porpoising, retraction turns, etc., can add a great deal of versatility, power and fun to your powder skiing, such moves can add complexity that you don't need when you're first trying to get used to the stuff. Similarly, a little speed is a good thing which will help you accomplish such moves with less effort (because the snow will help "float" the skis), but basic powder turns can be done fairly slowly. Whether such a static turn is really skiing the powder is certainly subject to some debate, but simplifying the movements will help you get started and gain some confidence.
I first skied powder at Berthoud Pass, Colorado some 20 years ago. Berthoud only averaged 500 or so inches per year in the 80's (according to the weather station up there, not the area management), so I guess it doesn't meet the Mt. Baker standard, but, for most of us, it'll do.
I also taught adult skiing at Winter Park, Colorado for a number of years, so I have a few credentials, though nothing even close to those held by a number of people who post here.
I now ski at Whitewater, British Columbia. It still doesn't meet the Mt. Baker standard for sheer quantity, but it does pretty well, and I've learned to ski wet Pacific Northwest goop as well as Colorado light and dry.
I ski on a K2 with a 78mm waist. According to some who post here, I'm probably gay. But I get more face shots on a smaller ski! Sometimes I retract (especially in the trees) and sometimes I just let 'em run deep.
To start skiing powder, you only need three things: 6" or more of ungroomed powder, enough pitch to actually move in whatever quantity of snow you have, and a willlingness to commit yourself to move downhill. The last one is more difficult than you might think, because there's a part of your brain that is not convinced that you can actually finish a turn and control your speed in this stuff. This results in all kinds of interesting moves as you attempt to twist the skis around as quickly as you do on the groom. So the slope needs to be carefully chosen so that it's steep enough to move but not so steep that it's intimidating.
In the powder, you don't get to twist, pivot or push your tails out unless you've gotten the skis up out of the snow somehow. But you don't have to. Simplify. The skis can be gently guided even when completely buried.
Start similarly to the way you started when you were first learning to turn. You want to build on what you're already able to do. Start straight down your shallow slope in your shallow powder. Tip your skis to the right or left (your choice) and make a long gentle turn to a stop. Have patience. The skis will turn. Keep the pressure fairly equal on both feet. Allow the turn to develop. Feel the resistance around your feet. Then do it again in the other direction.
Repeat, this time starting at a small angle to the fall line, so that as you start the turn, you're turning toward the staight down direction (you have to be willing to move downhill - tip the skis down the hill, etc. - see, you already knew this) and continue the turn until you're pointed across the hill enough to stop.
This is pretty basic, but the survival part of your brain is beginning to get the idea that you can have some control, and your muscle memory is kicking in, doing what you already know how to do.
After you do this several times, you will have accomplished a complete turn in each direction. You're ready to link a couple of turns.
As you approach the end of the first turn, instead of taking it all the way to a stop, tip your skis down the hill so that they will turn toward the fall line again. Allow them to take their time and make big round turns. They'll accelerate down the hill, but you're going to stay centered over your feet (maybe even pull them back a little) and you'll continue to turn until the line slows you down again.
In 6" of powder, especially if you're at high altitude somewhere, it will be almost the same as groomed snow. As it gets deeper or heavier, it will require more commitment to move down the hill, flatten the skis that are down there somewhere, and allow the tips to move toward the fall line. Still, have patience. It will work. This is about guiding the tips in the direction you want to go. Attempts to push the tails will be futile!
As you get used to powder and your speed starts to increase, you will become more dynamic. You can begin retracting before the transition, add more aggressive steering if necessary, especially while your skis are floating close to the surface, drive them deep deliberately just for fun and face shots, etc. But, in its most basic form, you can use what you already know. Your skis can be tipped and guided, even when the snow is piling up your front and over your shoulders!
To finish, an anecdote: A few weeks ago, I traversed with a friend over to a lovely chute. It was steep and had something like 36" of untracked freshies in it. It also didn't have any trees, because of relatively frequent slides, so we had lots of room. Blasting was done for the day, so it had been deemed stable.
The friend is an "old school" skier. He has longer, narrower skis, and he porpoises aggressively in powder. He went first, and had a great, fun run, leaving a track of many small, zig-zag turns.
When I went, I let my skis go deep and stay there. I made larger, rounder turns, but I didn't actually go any faster than my companion. The snow rolled up over my shoulders continuously the whole way down, until it flattened out and the trees closed in, so I slowed down. I added more retraction and more steering and skied for the spaces between the trees rather than rhythm.
I made half as many turns as my friend. Did I have half as much fun?