When sodium transfers one valence electron out, it gains a positive charge, not a negative charge.
Charged ions cannot exist independently in solution, so there's always a counter-ion. So the counter-ion for nitrate would be Na+.
So when you dump Sodium metal into, Metal Nitrate, depending on the reaction conditions you may get Sodium Nitrate and Metal from a displacement reaction or no reaction at all - you can refer to the reactivity series and electronegativity series if you're only considering ideal conditions.