By far the best tool I found was the online IDE [1]. Your program compiles to webassembly as you type it, and it plays in the browser. An interactive diagram is generated representing your program, so you can easily see if you made a mistake somewhere (though not always easy to see just where your mistake is).
I also learned by looking at the standard libraries' source code [2] and the online manual [3]. For the actual DSP knowledge, which I was learning at the same time and which isn't specific to Faust, I was reading J. O. Smith III's writings [4] (in particular, Physical Audio Signal Processing was most relevant to me).
I published my trombone simulator [5] as a web app but without the source. I haven't published the speech synthesizer or spatial audio stuff but I may in the future.
I also learned by looking at the standard libraries' source code [2] and the online manual [3]. For the actual DSP knowledge, which I was learning at the same time and which isn't specific to Faust, I was reading J. O. Smith III's writings [4] (in particular, Physical Audio Signal Processing was most relevant to me).
I published my trombone simulator [5] as a web app but without the source. I haven't published the speech synthesizer or spatial audio stuff but I may in the future.
[1] https://faustide.grame.fr/
[2] https://github.com/grame-cncm/faustlibraries/
[3] https://faustdoc.grame.fr/
[4] https://ccrma.stanford.edu/~jos/
[5] https://nuchi.github.io/trombone/