This great short video from the English National Opera shows you how a singer's breath becomes sound.

Vocal control is not a “gift” you’re born with; it is a skill you can develop. Speaking and singing rely on a system of muscles. Just like an athlete works out to sculpt their body for optimal performance, professional actors and singers work on and develop the musculature of speaking and singing. Just like muscles in athletics, the voice needs to be properly warmed up to prevent injury. Just like strength building in sports, the voice too can be carefully exercised with regular focused practice to make it stronger and have more stamina. Just like athletes practice their moves over and over to have complete control, singers work on fine details in their singing so that they have more control over a broad range of sounds and tones. And—a fantastic performance comes with the same adrenaline rush athletes get when they cross the finish line victorious.

The vocal apparatus—that is, the entire system that contributes to singing—includes four parts: airflow, a vibration source, the resonator, and the articulator.

Breath/airflow: The diaphragm and intercostal (rib) muscles draw air into and out of the lungs.

The primary muscle of breathing is the diaphragm, a dome-shaped muscle that is attached to the bottom of our rib cage. It engages and descends every time we inhale. This creates a vacuum in the lungs and air rushes in to fill that vacuum. When you exhale, the diaphragm relaxes and rises, and air rushes out. The rib muscles, abs, pelvic floor, and lower back get involved, as well.

When we talk about breath support, we are referring to the work the lower abdominal muscles do in contracting and allowing the diaphragm to be more carefully controlled. Control over that muscle system allows us to exhale slowly and steadily while singing, which results in a long, sustained, and solid tone.
Vibration source: As air passes through our vocal folds, they vibrate, creating sound waves. This is where we control pitch.

Our vocal folds (also called vocal cords) are found inside the larynx (voice box) in our neck, just above our trachea (windpipe). The vocal folds are two flaps shaped like the letter “V.” When we speak or sing, those ligaments vibrate to create sound. Our vocal folds are about the size and thickness of a penny, and are made up of ligament, muscle, and mucosal layers. Our vocal folds vibrate many times per second during singing, according to which pitch we make. The vocal folds are a delicate area, full of tiny blood vessels, and if you sing too hard and without warmup, you can damage the blood vessels and that can create scarring and damage.
Resonator: The voice resonates in the vocal tract—the throat, mouth, nose, and sinuses. The shape and size of our vocal tract determines our unique sound. We can change the shape to create tone quality, such as nasal, brassy, round, sharp, bright, covered, etc. We can also affect how loud our voice is and how far it projects.

We change the shape of our throat using muscles in our larynx.
We change mouth shapes by moving our jaw, tongue, lips, and soft palate.
We can open access to or close off the nasal cavity with our soft palate.
The face, the chest, and even the bones and skull also contribute to the resonance of our voice.
Articulator: Vowel and consonant sounds are made using tongue and lip shape. The image below shows where certain phonetic and consonant sounds sit when you voice them in English. Try saying some of the words you see in the image and notice where you feel the sound resonating inside your mouth. (There's an easy-to-read word list below the graphic.)

Table showing where specific phonetic and consonants sit when voiced in English

BILABIAL Wood Man Baby Spy	LABIO-DENTAL Very Fall	INTERODENTAL Breathe Thought	ALVEDLAR Zebra Dad Sad Top Butter Nope Light	POST-ALVEDLAR Red Should Asia	PALATAL Yes	VELAR Cat Go Sing	GLOTTAL Happy Uh-oh

Timbre: Choosing Your Sound

Our voice's tone quality, also known as timbre, is the result of choices that we make consciously or unconsciously. Decisions about how breathy, how forward or covered, how bright or dark you make the sound will distinguish your singing and make it unique and memorable as YOU. It is your vocal “fingerprint.”

Some musical theatre singers choose a bright, nasal-forward "Broadway" sound because they think that’s what they are “supposed” to sound like, but the result can sometimes be an absence of voice character. I am of the belief that you should sing in a style that is appropriate to the medium but also make it your own. Do the things that you do well with your voice. Bring out the things that you love about your voice and that others love about it, too. Use professional recordings as inspiration, but don’t try to mimic them. You won’t transcend unless you find your own sound.

Over time, learn to balance musical theatre conventions and style with your uniqueness—finding a place within your sound for everything you’ve ever loved musically.