Why do metal conduct electricity?

Answer 1

Steel, iron, copper, aluminum, gold, silver, Mercury, lithium and all other metals and most metal alloys conduct electricity very well compared to most other compounds.

With the discoveries in solid state physics of the 20th century we learned that metals are collections of atoms which have somewhat unusually properties of the electrons. In metals the outermost electron (sometimes two) of the atoms is not specifically associated with that one atom but is free to associate with atoms far and wide. We say these are delocalized electrons. Since the electrons are not attached to specific atoms, it takes very little energy to move them. As a result, any small voltage causes a large electron flow in a metal.

This movement or flow of electrons is called electricity so this is why metals conduct electricity.

Aside: Metals are not the only materials that conduct electricity, they just do it especially well, billions of times better that most materials. The details of the theory of electric conductivity were not understood until the discover of quantum mechanics and the properties of electron energy bands, but that goes beyond the essentials of this answer.

Answer 2

As metals are good conductors, they allow the electrons to pass through them. Hence they conduct electricity.

Answer 3

A lattice of ions allows valence electrons to move easily.