HBr is a strong acid so it will donate its H+ ion.
NH3 is a weak base so it will accept the H+ ion.
Since a strong acid is involved, the reaction goes to completion:
HBr(aq) + NH3(aq) → NH4+(aq) + Br–(aq)
Acid: HBr
Base: NH3
Conjugate Acid: NH4+
Conjugate Base: Br–