"A man eats an apple."
Translation:Ein Mann isst einen Apfel.
Every sentence has a part; Subject, which is what we're talking about; Verb, which is what the subject does; and the Object, which is the direction of the Verb. Ein Apfel is when it is by itself or is a Subject (the "nominative"); einen Apfel is when it is the Object (the "accusative")
Why "ein Mann" not "einen Mann" as Mann is Masculine so "der Mann" should become "einen Mann"?