Covalent bonds are those bonds in which the atoms between which the bond is present share electrons. Each element retains its electrons but shares with the element with whom it creates the bond.
To graph a covalent bond there are different structures, for example the Lewis structure, which indicates the electrons in the form of points, then the number of points of the atom will be the valence electrons that the element has. The symbol of the element is enclosed in a circle and the electrons are drawn on the circle. The electrons that are shared overlap between the circles of both elements. In the following example you can see what I just described: