Batteries are the components that have been very familiar to all. A battery convert chemical energy into electrical energy. Electrons are generated from chemicals inside battery.

Dry cell consists of zinc electrode dipped in Zinc sulfate solution and copper electrode dipped in copper sulfate solution. Two or more cells connected together form a battery.Take a incandescent lamp and positive end of dry cell is connected to one end of lamp and negative end is connected to other end of lamp through a switch.If you turn on the switch, lamp will glow. Since current flows through the wire, lamp is glowing. Electron (charge) flow from negative end of cell to positive end generates electric current.

Electric current is the phenomenon of a flow of electric charge. It can be defined as the rate of flow of electric charge.

I = dq/ dt

where dq is the change in the amount of electric charge in a time dt. It is noted that direction of current flow is always opposite to that of electron. SI unit of electric current (I) is Ampere(A).
Electric current is measured by using an Ammeter. For most electronic circuits milli Ampere (mA) unit is more commonly used since very less current flows through such circuits.