Question

what is magnetic field and what are the magnetic lines of force

Answer 1

The area where the magnetic effects are felt or attracted is called as magnetic field.
The curved lines which are used to represent magnetic field are called as magnetic lines of force.

Answer 2

The magnetic field can be defined as:

“A region around/surrounded by a moving electric charge or a magnetic material within which the force of magnetism acts.”

How does Magnetic Field occur?

If you are wondering how Magnetic fields occur. Well, it occurs whenever a charge is in motion. That being said if you apply more charge in the motion the strength of a magnetic field usually increases. Besides, Magnetism and magnetic fields are part of the electromagnetic force which is indeed one of the four prime forces of nature.