why helicopter floating/flying still in 3km above the earth surface, comes at the same point even after few hours in air. Is Earth fixed or?

It's because all of the helicopter's motion is relative to the surface of the Earth.
To explain:
- when the helicopter is on the ground, before takeoff, it is moving at the same speed as the Earth
- when the helicopter takes off, all of its movements are relative to its initial situation - that is, all of its movements remain relative to the surface of the Earth.

Consider when you are in an automobile speeding along the highway at 60 miles per hour. If you lift your arm to point forward, you don't have to move your arm at 61 miles per hour in order for it to move forward, because your arm is **already** traveling, with the car, at 60 miles per hour. Any speed you use to move your arm forward is speed *in addition* to the speed of the car.

Likewise, that is true of the car (or the helicopter) relative to the Earth. The car and helicopter **are already traveling at the very same speed as the Earth**. Only **a change** in the speed of the car or helicopter is noticed because they are *already traveling along with the Earth*, already traveling at "zero" velocity relative to the surface of the Earth before ignition.

All the previous answers are incorrect. This is Newtons First Law- the law of inertia. The Earth is spinning toward the East at almost 1,000 mph. Therefore, everything on Earth is also doing the same thing. This will remain unchanged unless an external force is applied to alter the inertia. If not then if you were to jump up into the air, the western wall of the room you were in would slam into you rather quickly. It does not because you and the room have the same inertia. However for people to jump out of moving objects they appear to move backwards. This is due to the sudden influence of wind resistance acting as a force in the opposite direction of motion. This force slows you down and makes you decelerate in relation to the vehicle you were in. To have some fun with this there is a video on YouTube that shows this. Just type in car and Bowling Ball. then you will see some kids in the desert playing around but forgot this principle.

Your update is incorrect.
I go to a major town by train. At a speed of 100 km/hr ( relative to the earth) I can jump up and down in the train repeatedly and nothing strange happens.
I can throw a special little frisbee ( made of rubber ) along the aisle. Just as I could if the train was stationary.
Or a ball.

So clearly all the evidence is that UNLESS there is a wind blowing then whatever speed the objects are moving at is irrelevant and unknown.
All that counts is the relative speed.

Now when the helicopter was on the earth it was moving at the same speed as the earth so this would also continue if it lifted off unless there was a wind blowing which would accelerate the helicopter in the direction of that wind.

On the other hand if the air is moving with the earth then even something that was NOT moving at the same speed as the earth would experience a force that would quickly bring its speed back to that of the air and consequently of the earth too.

The helicopter is stationary relative to the air surrounding it.
Assuming no wind, the air is stationary relative to the ground.
Therefore the helicopter is stationary relative to the ground.

To say it in a different way, the air is moving with the earth and the air is carrying the helicopter along.

Same reason air above the surface can be still - because the atmosphere has characteristics of a fluid, and the helicopter's position is embedded in that fluid, carried along with the planet's systemic rotational dynamics.