Question

what is the nature of magnetic lines of force inside the solenoid and how they are formed ?

Answer 1

i think the magnetic field line of a solenoid is the combination of the magnetic field line of the coils

Answer 2

Just look-up google image search for the pictures of
A. Magnetic Field of a single loop of current
B. Magnetic field of a solenoid

This shows the first responder above wrote the truth

Answer 3

The following file may help you:-))