Chemical bonds are formed by the sharing of electron densities between two atoms. The electron density of the atoms is held between the two atoms and attracted to the positive forces of both sets of protons in the two nuclei.
In Ionic bonds there is a large difference in electronegativity between the two atoms ( greater than 1.7) The large difference in electronegativity results in most of electron density being located next to the atom with the greatest electronegativity, and very little electron density being next to the atom with the lower electronegativity. This makes it easy for the two atoms involved int the bond to separate leaving one atom with a positive charge and one atom with a negative charge.
In covalent bonds there is no difference or a small differences in electronegativity. The electron density is more evenly shared between the two atoms. This creates a stronger bond between the two atoms that is more difficult to separate. Atoms involved in covalent bonding do not separate into ions.
Ionic and covalent bonds differ in the degree of sharing of the electron densities between them. Covalent bonds share the electrons more equally and are stronger. Ionic bonds share the electrons very unequally and can be broken into ions.