When making turns with my hydrofoil I can yaw the board and the foil in 3 different ways to initiate a turn:
1. Using the momentum of my upper body I can yaw the foil board using my legs and/or hips. For all of you who can not imagine or understand how this is done here is a good example: (body twisting/rotation initiating disk yaw starts at 1:10).
Yawing the board in such a way is best done with a light, short pocket board combined with an appropriate foil (mast, front wing...) - it is really easy and much fun. Of course it could be harder with some foils combined with big, long heavy foilboard.
2. I can yaw the foilboard easier when I use the support of the kite (via the harness or when leaning with my hands on the bar and as a result on the lines). In order to understand more easily how this is done just imagine that somebody is holding the waist of the woman in the previous video clip or that she is leaning agains the wall with her hand. In such a case the woman will be able to yaw the disc easier than using her body only.
3. I can yaw the foilboard even more easier if my kite is turning and pulling me through the turn. I will use the previous clip again for easier understanding - imagine that the woman is just standing on the disk and somebody, holding her waist or hand, starts to rotate around the disk - of course the woman together with the disk will also start to rotate (disk yaw).
If you watch some video clips of Kai Lenny or anybody else hydrofoiling without kite you will clearly see how they jaw the board to initiate turns only using their bodies and if you watch (as already suggested) some Cloudfoilig clips you can see yawing the board using the kite for support or following it through the turns.
In order to keep my balance when hydrofoiling I also control the pitch of the board (in order to control the height) and I roll the board in two cases:
1. I roll the board to the inside of the turn in order to compensate the centrifugal force - the faster I move or the tighter I turn, the more I lean.
2. I roll the board when I foil upwind and I lean against the kite in order to withstand the pull from the kite.
People have difficulties to turn the hydrofoil because of 2 main reasons:
1. Wrong roll control. Either they try initiate the turn by rolling the board and they loose balance or they turn the kite but can not compensate the centrifugal force during turning with correct board roll, they loose balance and fall. I will use bicycle analogy to explain this. If you lean the bicycle without steering in the same direction you will fall. If you steer the handle bar to make a turn and you do not lean enough/or you lean too much to the inside - again you will fall.
2. Wrong pitch control during the turn. Most kiters are used to apply more back foot pressure when turning and even when they manage to foil in straight line with correct pitch control they instinctively lean to the back foot when they start to turn and of course they fall.
To summarise how I understand turning the hydrofoil - I yaw the foil board in order to initiate the turn and I control the roll of the board (in order to compensate the centrifugal force) together with the pitch of the board (in order to control the height).