I'm not going to bore you with the intricate details, nor am I going to paste graphic pictures of Vocal Folds. Nobody really wants to see that. So, instead of all of the mumbo-jumbo that I have to know as a teacher, I'm just going to break it down simply so that you know all that you need to know as a student! If you have had lessons from me you will hear me say phrases like "use the diaphragm more", "smile through the note" and "remember to use your breathing more!". This is because, when you sing (and talk) you have 3 fundamental things you do and use:
The power of your voice comes from the airstream the lungs provide. The air stream provides the energy for the vocal folds/vocal cords in the voice box to produce sound. The stronger the airstream, the more powerful the voice.
The diaphragm is a muscle which helps manipulate how you use the air in the lungs to produce that sound. For example, if you needed to belt out a note you would take a big breath, and pull in on the diaphragmatic muscle in a sharp motion to provide that power.
The voice box contains two vocal folds (also known as vocal cords) that open when you breathe and close when swallowing. When singing/using your voice the airstream passes through these folds and they set into vibration. As a comparison, the vocal folds are like a mouthpiece of a brass instrument - on their own they would sound like a buzzing noise - but with the rest of that brass instrument added to the mix, or in our case, resonation, it creates our sound!
Also worth noting, whenever someone says that the voice is an instrument, you now know why!
All of the structure above the vocal cords (the throat, nose, and mouth) creates the musicality of our voices by changing the shape of the buzzing sound (the voice box creates) into something pleasant and lovely to listen to.