I assume that this answer is explained to a layman and so I will try to explain it from the basics.
Let’s start by understanding the question, “How does a DC motor work?”
What does engine operation mean? It simply means how an engine works.
What can cause an otherwise stationary object to move ? A force must be applied to an object to move it.
If the motion is rotational , the corresponding force is generally called “torque”. Therefore, for the engine to work, torque must be produced.
The real question now becomes simple, ” How is torque produced in a DC motor ?”
So we give DC voltage as input to DC motor which has two types of windings: armature winding on the rotor ( rotating part of the motor ) and field winding on the stator ( fixed part of the motor ).
So DC input is actually given to both coils which then carry DC current. (flows that are one-way and their average is non-zero in any given period of time)
Basics: A current-carrying coil creates a magnetic field in the space around it. Two magnetic fields interact with each other in space and force or torque is applied to each of the two coils and creates two magnetic fields.
In a DC motor, two magnetic fields are caused by the DC currents given to the armature and field windings.
A counter torque is created due to these two magnetic fields from the armature and the field, which drives only the rotor carrying the armature windings while the stator remains stationary. This is due to the mechanical arrangement of the stator, which is fixed and the rotor is inside, facilitating its free rotation under torque.