Imagine that you're at a cocktail party. There are groups of people around the room having conversations, but you're focused on what your friend standing in front of you is saying, and all the other conversations are tuned out.
But if someone were to say your name in a nearby conversation, you would automatically transfer your focus from the conversation in front of you to the one in which your name was mentioned. How does this happen?
Were you listening to the other conversation at the same time as you were paying attention to your friend?
Yes and No. You were only listening to your friend's conversation. Your unconscious, however was listening to every conversation in the room.
It simply kept those other conversations out of your consciousness because they weren't relevant. But it was still actively listening to them to see if anything relevant to you appeared, at which point, it served up that information to your conscious mind.