An ionic bond is formed by the attraction of oppositely charged atoms or groups of atoms. The most common ionic bond if NaCl, which you know as table salt.
A covalent chemical bond results from the sharing of electrons between two atoms with similar electronegativities.
For example, a double covalent bond, which occurs in ethylene (C2H4), results from the sharing of two sets of valence electrons.
Electrons are said to be delocalized (not found in one specific region, such as between two particular atoms.)
Delocalization can be used to explain conductivity, malleability, and ductility.