"Have an apple."
I think it might be confusing to some people to learn to translate "avoir" as "have" instead of "to have". It should be learned as the infinitive.
When I hear or read "have an apple" I understand this is an invitation (imperative), to be translated in French by "prends une pomme" or "prenez une pomme".
same thing: for me it's a imperative and I translated it as "prends une pomme"
In French the imperative with "have" would be "Aie une pomme" The subjunctive form is "Que tu aies une pomme" (sing) or "Que vous ayez une pomme" (polite sing and plural)