"You have an apple."
Translation:Jij hebt een appel.
"U" is the formal version of 'you', it is used when addressing strangers or to show a certain kind of respect.
"Je" vs "Jij" is a more subtle difference. You can read about it here. In short, "jij" is used to emphasize the fact that YOU are doing something, not somebody else. "Je" does not carry such emphasis. It is a little bit like in Spanish, where you can leave out the pronoun ("tu") as a subject, or include it for emphasis.