An electron is a lepton and a negatively charged elementary particle that is typically found in the orbitals of atoms, orbiting around the atomic nucleus. Electrons orbit the atomic core because of their negative charge that attracts the positive of protons. Electrons have a mass about 1,836 times smaller than the mass of protons.
One use of electrons is to allow atoms to bond. If an atom has too many electrons in one of the atom's shells, then it will give up an electron to another atom that needs electrons, forming an ionic bond. Another way atoms can bond also involves electrons. Atoms can "share" electrons, allowing both atoms to fill the gaps in their shells.