1, look around the appearance of the submarine, the little boat, and the interior of the submarine, there are icbm and many guys there
2, change location to water takeoff position from the default locations list
3, restart game to be born from the water takeoff position, so to let the little boat to not be upside-down, as the engine and air inlet can not be buried under sea surface
4, watch the altitude of submarine carefully, it will descend at very high speed at first, but the speed will drop down, until at a steady diving speed of about two feet a second, there's no limit of diving altitude
5,  to stop descend, push throttle forward little by little, otherwise it will lift up quickly. 
6, before you can drive freely, something must be done. First, throttle must be pushed to get some speed forward, so that the submarine can be operated. Then, activate button 1, to activate the particles
6, how to drive the submarine? Use your joystick, push to pitch down so to dive, pull to pitch up to lift, roll joystick left to turn submarine left, roll joystick right to turn right submarine. As real submarine, it do NOT have roll movement, so, The roll operation of joystick is assigned to turn movement of submarine, and nothing assigned to pedal operating. Above all, all you need is to handle your joystick, if running on iPad, just hold your iPad to drive it!
7, As the submarine is under sea surface, and the view point is detached from it to above sea surface, it's very hard for you to get situation awareness. One hint is the altitude number on the HUD, it tell you the depth, then the speed meter tell you the speed, the most important hint, your viewpoint will be attached to the surface point vertical above the submarine, so, you can tell out where submarine is going
8, push the vtol slider to forward 100%, push throttle forward to 100%, too, these are preparations for launching missile
9, press button 2, the missile is launched, it will penetrate the water and fly into the sky! You don't need to come up to sea surface to launch, but if you dive to deep over about two or three hundred feet, the missile may not be able to penetrate sea water. After lauched missile, you should pull vtol slider down to middle position, to close the lid of silo on the back of the submarine