How does a galvanometer use a magnetic field to indicate the strength of an electric current?

An electromagnet of a spring is placed between the poles of a permanrnt magnet. when there is current in the coil, the resulting magnetic field lines up with the field of the permanent magnet, and indicates the strenght of the electric current by deflecting a needle on a dial.

A Galvanometer is an instrument that is being used for detecting electric current. It contains an analog electromechanical actuator that produces a deflection that is a somewhat response to the electric current through its coil in a magnetic field.