Computers can’t read continuous signals. Instead they need digits, blocks of information which they can process.
Sound wave vibrations in the air are continuous streams of information. Therefore, for computers to be able to understand sound wave information they need to convert this continuous signal into blocks of information which they can process.
They do this by taking a snapshots of the sound wave at a specified rate. The more chunks that the computers store every second, gives a more accurate picture of the sound wave.