Electricity is a type of Energy which involves the flow of electrons. All the matters are made up of atoms and the center of it is called Nucleus. Nucleus has positively charged particles known as Protons and uncharged particles known as Neutrons. The Nucleus becomes surrounded by negatively charged particles known as Electrons. Electrons revolve in a circular orbit known as a cell. The charge of electrons and protons becomes equal and opposite in nature. So it maintains equilibrium within the atom.
When that equilibrium force between protons and electrons is disturbed by any external force (Electric Field), then atom may gain or lose electrons. When electrons are lost from an atom, then the free electrons move toward the Electric field. Hence due to the free movement of these electrons, electric current flows through the conductor in opposite to the direction of the flow of electron.