SOURCE                       LOAD

                               battery                           amplifier
                               amplifier output            loudspeaker
                               microphone                   amplifier
                               motor                              lathe
                               dynamo                          lamp
                               legs                                 bicycle
                              supply                             cooker

Current flows out of the source through one lead, through the load and then back to the battery via the other lead.

The value of the current flowing back to the battery is exactly the same as that leaving. Nothing is lost or gained.

To protect the load and source against excessive current flowing due to a fault, a fuse is inserted in one of the leads.