Atoms are the smallest building blocks of the universe (like lego bricks). They are made up things that look like earth: a nucleus in the center and electrons spinning like moons. In chemistry, electrons are important for sticking atoms together. In a non-metal solid, there is usually a grid of atoms, some like to keep electrons to themselves, and some prefer to have less electrons – this makes the atoms line up positive to negative like a magnet. In a metal, the electrons are shared amongst all ALL atoms – like a sea of electrons. This means that electrons can flow like water all around the metal – this is why an electric charge can pass through iron (where the electrons are free to move around). Electricity is not very good at passing through plastic or rubber, because the electrons are held by the atoms in the rubber.
It is a very good question!