Some kinds of atoms have electrons that are loosely attached. They can easily be made to move from one atom to another. When those electrons move among the atoms of matter, a current of electricity is created. This is what happens in a piece of wire. The electrons are passed from atom to atom, creating an electrical current from one end to the other, just like in the picture to the left.
Electricity flows through some things better than others.
How well something conducts electricity is measured by its resistance. Resistance in wire depends on how thick it is, how long it is, and what it's made of. The lower the resistance of a wire, the better it conducts electricity. Copper is used in many wires because it has a lower resistance than many other metals. The wires in your walls, inside your lamps, and elsewhere are mostly copper.