A water start (also called a board start) is the critical skill to learn when you have mastered controlling your kite and body dragging. This will be your first real taste of kitesurfing.
The steps are (for a water start to the left):
First lie backwards in the water with your board on positioned downwind with your kite at 12 O'clock
Check that there is nobody in the way in your direction of travel
Angle the board 45 degrees to downwind and keep the left tip out of the water
Move your kite slightly backward (away from your intended direction of travel, e.g. to 1 O'clock)
Turn your kite in your direction of travel and dive it forward. The deeper you dive the kite the more power it generates.
Start with a short dive so that you are underpowered - you will get lifted out of the water then fall backward. Avoid getting overpowered - which will pull you forward over your toes.
Once confident with handling the diving kite, try a more powerful dive so that you get lifted right out of the water.
Hang on to the bar as you get lifted out of the water and start planing downwind to gather board speed. If you are going too fast just PUSH OUT THE BAR.
Straighten your front leg once the kite pulls you are out of the water.
Let the board run downwind to get up some speed.
Look where you want to go (not at your kite). This will get your body oriented in the right direction and assist with edging the board.
Edge the board with your heels in your direction of travel.
Lean back a bit to avoid getting pulled over your toes.
Fly the kite back up after the dive, but not too high - if you continue the dive it will crash into the water.
Keep the kite flying - by now you should be bringing it back down again to generate more power, or have it locked in position if there is good wind.
Once you are up and going concentrate on balancing the power of the kite against the rail of the board. That's it. You are kitesurfing!
If your board sinks you need more power and board speed. Keep your kite turning and don't let it get too high. Make sure you get enough board speed before edging the board.
If your kite crashes into the water, start turning it back up earlier. This will become automatic eventually.
Do not bring your kite to 12 or you will lose power and speed and your board will sink. Keep your kite at 9-10 or 2-3
Keep your knees bent when you start to lower your centre of gravity.
In stronger winds you don't need to fly the kite down so hard, and you won't need to fly it up and down (sine wave). You will be able to fly it "locked in" at a convenient position.
Avoid pointing the board too far upwind and/or choking the kite (bar in too much) - both will result in your kite losing power and you sinking back into the water.
Heading straight downwind will also cause the kite to lose power - you counteract this by edging the board.
If your location suits try a downwind run to get the feel of board speed and flying the kite.
This video shows a water start at the beginning, and a few later on during the kiting session.