Covalent bonding describes the process where two atoms form a bond by sharing one or more electrons in order to fill up their outer orbital and become more stable. Covalent bonding typically occurs between two non-metals, which are mostly located on the right side of the periodic table.
A covalent bond can either be polar or nonpolar, depending on the electronegativities of the two atoms involved. The electronegativity is a measure of how strong an atom can attract an electron. If the atoms forming a covalent bond have different electronegativites, the strongest atom will have a slightly negative charge at the site of the bond, while the other atom will be slightly positive.