How can an airplane fly with single propeller without rolling over?
When it is slow, the two or three wheels should keep it from flipping over.

Once it is fast enough to fly, the wing will provide what we engineers call roll damping: Any tendency to roll† will cause an opposing moment which will stop the motion quickly. The rest is done by a differential deflection of the ailerons, so the wing creates an equal and opposite rolling moment to that of the propeller.

What is roll damping: Once the wing starts to roll, one side will go up while the other goes down. This will cause a change in local angle of attack and, consequently, local lift. The down-moving wing will see a higher angle of attack and a local lift increase, and the opposite happens on the other side. Total lift will remain unchanged, but now the change in the spanwise lift distribution will lift the down-moving wing back up and vice versa. The movement stops before it could pick up any speed.

With powerful engines, engine torque is a real problem and needs to be canceled with a few tricks:


Camber on the vertical tail: The vertical tail will create a side force and rolling moment which depends on the speed of the air flowing over the vertical. This helps to make the correction depend on the power setting of the engine. Just make sure that the vertical is in the slipstream of the propeller.
With contra-rotating propellers you can cancel the rolling moment of each propeller with that of the other. This needs a more complex gearbox, however.
In operation, apply power changes only slowly. With its narrow undercarriage, the Me-109 would become uncontrollable if the pilot went from idle to full power on the ground too quickly.
Watch the gyro forces of a spinning propeller: In taildraggers, the aircraft will yaw due to gyro forces once the tail is lifted during the ground run or the pitch attitude is changed in flight. Also, yawing (rotation around the vertical axis) will create a pitch moment (which acts around the spanwise axis).


† Roll: Movement around the longitudinal axis.