The drawing on the left side, is supposed to show an example of one hydrogen nucleus that has a bond to another hydrogen nucleus. (No picture has been taken of a bond between two (hydrogen) atoms; There is no evidence of any expert having seen (with the expert's own eyes) a bond between two atoms.) Those two nuclei are inside the electron cloud (that is made of the electrons of both of these two hydrogen atoms). To show when two atoms have a covalent bonding, one can put a line - on a drawing - between the nucleus of the one atom, and the nucleus of the other atom.