When flying, Ctrl (Control) causes you to descend and Space causes you to ascend. Double-tapping Space will exit flying mode, causing the player to fall under gravity (be warned that you will take damage if you have damage enabled).
Flying in Minecraft for the pocket edition version is just like the full version. Double-tap the middle button or the jump button. To go up higher, hold down the jump button while holding down the up button.
To stop flying just double tap Spacebar while you are in the air.
If you mean in Creative Mode, you double-tap the space bar. Or hold down left shift and or press the s button
Shift
In creative mode, when you are flying, you hold space to fly up and shift to fly down. That is, if you haven't changed the controls. If you did, the key you use to sneak is the same key to fly down.
To stop flying in creative mode double tap space
Double tap the jump key to begin flying, double tap again to ascend double tap down to descend.
do what you do to go up or hold crouch
Double tap the jump
don't know yet
In Minecraft, to descend while flying, simply press and hold the "S" key (or the down arrow key) on your keyboard. You can also use the spacebar to ascend and control your flight height. Additionally, if you're using a controller, you can pull down on the joystick to go down. Just be mindful of your surroundings to avoid taking fall damage when you land!
Inf flying, unlimited resoruces and godmode.