What is the difference between the Setup Guide and the script Bitwarden.sh?

Hello,

I’m trying to install a self-hosted server and I don’t understand what the difference is between the Setup Guide (Setup Guide | Bitwarden Contributing Documentation) and the script ./bitwarden.sh available in the git repo.
It seems that both have the objective of setting up the server but in different ways.

So I would like to understand what the difference is between these two solutions and which of the two I should use.

Thanks for your help.