Do you want to setup Lemmy for development, or to run a production instance? We have docs for both, so please try to follow those, and explain where exactly you are getting those problems.
The mdbook error means that it couldnt find the documentation, but Lemmy works fine without that.
https://lemmy.ml/docs/en/administration/administration.html
https://lemmy.ml/docs/en/contributing/docker_development.html