If you think of a digital picture, you essentially have a bunch of tiny, single-color pixels which, when put together, make a pretty good recreation of whatever you take a picture of. The same is true for a digital audio file, it’s essentially a ton of tiny “pictures” of the audio signal and when you put them together and play them back, it’s a fairly accurate and sometimes exact replica of the original audio, depending on the audio format. You have an analog-to-digital converter which takes in the audio as input, and separates it into millions of tiny pieces of sound, often 44,100 times per second. Each of these tiny pieces is an approximate record of the sound of the audio signal during that fraction of a second. When you play an audio file, the computer stitches all these tiny fragments back into a continuous sound which is played by a speaker.