The main difference between ionic and covalent bonding is that ionic bond is formed between two ions and covalent bond is formed between pair of electrons.

Ionic bonds :  Ionic bonds involve a cation and an anion. The bond is formed when an atom, typically a metal, loses an electron or electrons, and becomes a positive ion, or cation.One example of an ionic bond is the formation of sodium fluoride, NaF, from a sodium atom and a fluorine atom.

Covalent bond: A covalent bond consists of the mutual sharing of one or more pairs of electrons between two atoms. These electrons are simultaneously attracted by the two atomic nuclei. A covalent bond forms when the difference between the electronegativities of two atoms is too small for an electron transfer to occur to form ions.