One "end" or "terminal" (or node or electrode) is made of a substance that pulls electrons chemically from the ("electrolyte solution") substance in the battery, and the other terminal is made of a substance which gets the electrons pulled from it, into the substance inside the battery. So, chemically, it causes a current from one terminal in the battery (the one that pulls the electrons away from the stuff in the battery), through a circuit (a radio, a car, a light, or whatever), and then as if back around through the battery again, until it runs out of the "charges" ("positive" and "negative") that the substance inside has.