The relationship between the two is that it can determine the classification of an atom. The number of neutrons determines the isotope and the protons determine the chemical element. An atom can also be considered electrically neutral if it has an equal number of electrons and protons. This is according to information from, http://en.wikipedia.org/wiki/Atom.
Electrons have a negative charge, and protons have a positive charge. If you have one more proton than electron, you have a (+1) charge. If you have one more electron than protons, you have a (-1) charge.