how rotating magnetic field produced in induction motor?

the induction motor does not have any direct supply onto the rotor; instead, a secondary current is induced in the rotor. To achieve this, stator windings are arranged around the rotor so that when energised with a polyphase supply they create a rotating magnetic field pattern which sweeps past the rotor. This changing magnetic field pattern induces current in the rotor conductors. These currents interact with the rotating magnetic field created by the stator and in effect causes a rotational motion on the rotor....hope it clears your query

This is an explanation of the Induction motor principle in layman's terms.
Lets discuss a 3phase motor. The stator is wound with 3 phases placed 120 degrees apart. R gets a supply. At that time fraction, the rotor conductor near the R phase becomes a magnet of the opposite polarity. Now, the supply moves to the Yphase from R phase. But this transition takes lesser time compared to the dying out of the polarity of the conductor near the R phase winding. So, the conductor near the R phase is pulled to the Y phase part of the stator. This happens again in the transition from Y to B and B to R. Thus the rotation continues for the rotor. and we get a continuous rotation in a synchronous speed [which can be found out by speed N=120*(frequency of supply)/(number of poles)] In a single phase motor, we give another winding which passes current through it with a lag compared to the first winding.