I can answer your question in terms of psychology.

Developmental psychologists have argued a lot about this question. One idea is that there is a Critical Period early in life when the brain is best set up to acquire learn should it be present in the environment. Scientists who support this idea think that the major parts of language, like grammar, are built into a special psychological mechanism called the Language Acquisition Device that’s active only at an early age. The brain therefore limits the possible features of language, making it possible for a child to learn just by listening to others speak.

We also know the major brain areas that enable human speech. In most people the left hemisphere, or side, of the brain contains areas that specialize in language production and language comprehension. Broca’s are is responsible for language production, or controlling the muscles that allow you to speak. Conversely Wernicke’s area is responsible for language comprehension, or understanding what spoken (and written) words mean and putting them in a sensible order. The two areas work together to enable human speech.

Damage to these areas causes a condition called aphasia. In Broca’s aphasia people cannot articulate words correctly, producing nonsensical words that nevertheless seem to fit the structure of a sentence. In Wernicke’s aphasia people say words perfectly clearly in phrases that lack clear meaning and grammar.

Vocal chords (actually flaps) in the trachea make sound when air passes through them much like a musical instrument such as a violin. The shape of your mouth, position of your lips, etc., then modify the sound coming out of your trachea.