Radio wave interference
How does the wave gets overriden?


In AM radio, this is mostly a matter of perception. Imagine one person shouting in your ear and another person whispering on the other side of the room. Mostly you'd hear the shouting person. You could say they had "overridden" the quieter speaker. 

In FM, the modulation scheme actually does tend to favor receiving a stronger signal and reduces the effect of interfering signals. This is a reason for the higher fidelity of FM radio. 


  How can one emitter be stronger than another if there, for example are equal distance from the receiver and from each other?


They could be broadcasting with different power levels. All else being equal, a 100 kW station will produce a stronger signal than a 1 kW station if the receiver is equidistant from them.

They could be broadcasting with different antenna radiation patterns. Radio broadcasters will use antennas that transmit preferentially in certain directions in order to deliver their signal to more populated areas. If you are in the favored direction from one station but in an un-favored direction from the other transmitter, you could receive a stronger signal from the first one.

There could also be terrain effects or other impairments reducing the signal received from one station or the other, even if their source power is equal.