If you really listen late at night after everyone's asleep, you'll hear the noises your house makes — the creaking of walls and floors, the hum of the refrigerator, the banging of the radiators.
When you listen to something, you don't just hear it, but you really pay attention to the sounds. You can listen to music, listen for the sound of your guests arriving, or listen to the advice your grandfather gives you. The phrase listen in means to eavesdrop on, or deliberately overhear, a conversation. The t in the middle of the word listen is silent (you can't hear it even if you listen).