Is there good documentation somewhere for working with promises? I don't really understand what they are.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Using_promises may help

@late-lizard-19909 are you referring to javascript promises, or Pulumi promise like outputs? for the latter, I wrote this: https://leebriggs.co.uk/blog/2021/05/09/pulumi-apply