There are nitrogen functions in a high oxidation state that can de reduced to give amines.
Reduction means the grabbing of electrons from another species that sumultaneously oxidizes.
Metals are excellent for this purpose.
The substitution of a good leaving group by cyanide leads to nitriles whose reduction yields amines - with one more carbon!!!
Amides ('with D') render amines ('with N') by reduction:
Ammonia and amines are nucleophiles that could attack aldehydes or ketones. If one introduces a reducing agent in the reaction medium, the intermediate imine is reduced in situ leading overall to a new amine.
