What is the immediate cause of liftoff?
As the elevators rotate to get a negative pitch angle to the horizontal (moving the tip of the elevator upwards), a pressure difference is created causing it to produce a downwards force, and as a result the aircraft pivots around the landing gear, rotating upwards.
As it does so, the wing starts to generate more lift, as can be
seen on the graph below. The higher the angle of attack- the more
lift, since the lift coefficient becomes higher, up to where stall starts.
When the lift exceeds the weight, the aircraft will lift off.




For taildraggers, the tail is normally rotated up at a low speed while the aircraft continues to accelerate, and once a sufficient speed is reached, the tail surface is again lowered, causing the wing to increase the AoA and to lift. Footnote: If I'm not mistaken, this is more of an act to improve control and reduce drag, since at some point the aircraft will lift off on it's own with it's tail-down angle of attack.