Consider a point on a wire. As the current gets going, the current at that point will go from zero up to the final value over some (small) period of time. The m

Consider a point on a wire. As the current gets going, the current at that point will go from zero up to the final value over some (small) period of time. The magnetic field around the wire at that point must also grow from zero to it’s final strength over that period of time. The growing magnetic field causes a current in the wire flowing in the opposite direction as the first current. This slows the flow of current in the wire (so that it doesn’t happen instantaneously), and it’s also the source of the energy in the field; it’s called the self–inductance of the wire. An inductor in a circuit is just a coil of wire so that the magnetic fields from many parts of the wire all reinforce each other and cause a larger opposing current in the wire.