Fourier showed how many different graphs, not just the graph of sound can be built out of combinations of the sine wave.

One needs to know the frequencies of the different sine waves and how loud they are playing. Then by adding up the heights of all the waves we get the original graph. This is called Fourier analysis.

How does a CD work: it tells your speaker to play all the sine waves with these different frequencies together. The combination produces the sound of a violin or clarinet or more complicated sounds.

What Fourier had shown is that playing tuning forks of different frequencies together is sufficient to reproduce any sound you might record.