How does a DC Generator work?

 ANS:
D.C. generator works upon the principle of Electromagnetic induction that includes both Faraday's laws and Lenz's law.
To understand the working of a D.C. Generator,it is logical to get first get a brief idea of its construction part.
The D.C. generator(or any D.C. machine) has the following parts:

Stationary members(Stator)
Stator frame
Stator core
Field windings
Brushes

Rotary members(Rotor):
Armature core
Armature windings
Bearings

Now,the working of the generator can be explained as:
The field windings are provided with a current so as to develop a magnetic field around the armature(rotor) of the generator.This phenomenon is also known as field Excitation.
When the armature is made to rotate with the help of any prime mover in the magnetic field as generated by the stator side,an emf is induced in the armature.The magnitude of this generated emf is given by Faraday's law while the direction is given by Lenz's law.
When the armature windings are connected to any load,an electric current begins to flow.
In this way,a DC generator works.