What is the ionic bond formation of NaCl?
It is an ionic bond created by an attraction between the +1 sodium cation and the -1 chlorine anion.
Sodium which has an electron configuration of $$1s^22s^22p^6$$ and $$3s^1.$$ The sodium will readily give away the one electron in the 3 s orbital in order to stabilize the outer shell and become like the noble gas neon. In doing this the sodium takes on a +1 charge with 11 protons and 10 electrons.
Chlorine has an electron configuration of $$1s^22s^22p^6$$ and $$3s^5.$$ The chlorine will readily take on an extra electron to fill the 3p orbital and become like the noble gas argon. In doing this the chlorine takes on a -1 charge with 17 protons and 18 electrons.
As Paula Abdul told us in the 80's "Opposites Attract" and when the charges are equal and opposite the atoms are held together with an electrical attraction of a +1 cation and a -1 anion.