I think the interesting thing here is the way the position of the stress changes the sound of “are you”, because these words are weak, or unstressed. “Are” becomes /ə/. You need a very relaxed mouth for this sound. Your mouth should be just slightly open, with your tongue relaxed, and neither front nor back. Just make a little noise with your voice.
“You” is pronounced with the same vowel sound. Try putting them together now.
The phrase is an informal way of saying “How are you?”. You can use it to greet a friend.