So ammonia, #NH_3#, has 8 valence electrons to distribute. 6 electrons are utilized for the 3 #N-H# bonds, and the remaining 2 are localized on the nitrogen as a lone pair.
So we get #:NH_3#. Note that this is not the end of the story. Why have I represented each atom in the molecule as neutral? If I had ammonium ion, #(NH_4)^+#, the positive charge is associated with the nitrogen centre. For the nitrogen in ammonia, there are 7 positive nuclear charges (i.e. 7 nuclear protons). This charge is balanced by 2 inner core electrons, 2 electrons from the lone pair, and 3 electrons from the #N-H# bonds (i.e. the other electron in the #N-H# bond is formally assigned to the hydrogen).
