Why you instead of they?
Sie(with a capital S) is a polite (you)
Of course you can use du siehst
I had to guess this from sound alone - how can you tell it's "Sie sehen" and not "sie sehen"?
But here we have no context. Presumably 'They see the apple at the restaurant' is also an acceptable translation.
I couldn't get this one to understand me. I tried maybe twenty times.
It's probably the restaurant word. The second part is a bit different from english and when you say it it sounds like "restuhont" :D.
Although I am sure German people would understand if we pronounced it exactly like it's English version.