All you have to do is get the apple in your hand as if you were going to mine with it.
Then hit the LT trigger if you NEED to eat it. (As in if your health is low)
Chat with our AI personalities
Hold down whatever you have place block binded to
Yes you can get Minecraft on an Apple Mac.
I do
There are no apple trees in any Minecraft versions, but in the latest update of Minecraft for Xbox apples drop from tree leaves.
Grass, Probably.