History Of Sound Questions

Question 1. How did they record sound with just light?

I understand how they actually recorded the sound, they used a sound sensitive light bulb to project light onto the light sensitive film. The main thing that I'm confused about is how the sound was played back. If it was just light waveforms on a piece of film, how does that create sound?

Question 2. How would they playback the recorded sound?

Would the sound come directly out of the projector through and amplifier? How would the sound on the film be read and made into sound? When I try to think about it, it doesn't make any sense in my brain. Also, how did optical sound improve in quality? When you listen to an old movie, you can immediately understand that its an old movie right when you hear any sound. How did they improve their sound quality?