Is the production of electricity by magnetic field.
There are two types of generator which is D.C generator . And A.C generator
A.C gen consist of rectangular coil,brushes and permanent magnet
According to the external force mechanical energy used to rotate coil, due to magnetic flux produced by permanent magnet create induced current, this is to according to flemmings right hand rule of electromagnetic induction the rotating coil will produce current
I hope that will help.