The speech sounds are referred to as consonants and vowels.
Linguistically speaking, the distinctive speech sounds are called phonemes, which are explained in more detail in the chapter on phonology. You cannot use isolated phonemes for communication, because phonemes are by themselves meaningless. But we can assemble and reassemble phonemes into larger linguistic units. These are commonly called “words”. Although our capacity to produce new phonemes is limited, we frequently coin new words. Hence, our capacity to produce vocabulary is unlimited.