Yup, that's fair enough.
But here's what I consider the core parts of Danbooru:
- The Ruby interpreter
- Ruby Gems
- Rails
- PostgreSQL
- The server
At minimum, you would want to retrieve the Danbooru source. Go to a terminal, and type this in:
svn co svn://donmai.us/danbooru/trunk danbooru
Then run the following to install Ruby, Ruby Gems, PostgreSQL, and Ruby On Rails:
sudo apt-get install ruby rubygems postgresql-8.4
sudo gem install rails
Note: Danbooru was made to work with an older version of Rails, and PostgreSQL 8.3, but I've still gotten it to work on the latest versions.
Now, cd into the directory, and run:
rake gems:install
This will attempt to install the gems required by Danbooru. You will probably run into some errors, but you'll at least have a good chunk of the software you need now.
There is also still a matter of missing packages that you need installed. But since the script is unvailable, I don't know what they are, and can't help you with that (I really should've saved a copy of it, or took note of the required packages). But if you had the script, it could've automated the entire process of setting Danbooru up for you - all the way from downloading and installing the Ruby interpreter, Ruby Gems, Rails, getting the Danbooru source, and setting-up the database.
So, now, learn the following: Ruby, the Ruby on Rails framework, and SQL/PostgreSQL. I'd also suggest looking at the documentation that comes with the Danbooru source. It's probably out-dated, but it might still prove useful.
Once again, a cautionary note: If you want to deploy a web application, be prepared to learn a variety of skills, and encounter challenges.