"I always give the teacher an apple."
Translation:Ik geef de lerares altijd een appel.
They can both mean the same thing: a teacher. Although "leraar" really means "teacher", and "docent" is mostly (but not exclusively) used to describe a college or university teacher.
Do note however that "leraar" is the masculine form of "leerkracht", which is neither masculine or feminine. The feminine form of "leerkracht" is "lerares".