When a current is passed through a conductor, a magnetic field is created in its surroundings.
We can represent this magnetic field by drawing 'field (or 'flux') lines' with two characteristics
1. The density of flux lines illustrates the relative strength of the magnetic field
2. The direction of arrows attached to the flux lines represents the direction of the magnetic field.
Both of these parameters are important in deciding the magnitude and direction of the force created between a current carrying conductor placed in the magnetic field.