Y is a YAD7 / Drupal 7 module and so it is installed like most Drupal 7 modules. There are many guides on how to install a Drupal 7 module.
Y differs from other modules in that it makes heavy use of the PHP YAML extension. This extension is not included in many PHP systems (including Pantheon Drupal 7 sites), so a little extra work is needed to install it.
The PHP YAML extension is very easy-to-use. It is written in C, so it is also very fast.
Here is a guide for installing the PHP YAML extension.
If you will be running Y on a server that lacks the YAML extension, you can still do so provided you first invoke your webserver from a development machine that has the YAML extension installed. When Y locates YAML files, it translates them to JSON, just in case it might be useful. If you add the JSON files to your website source code and upload it to your server, the server will find and use the JSON files. This is the technique needed to use Y with Pantheon web-hosting.
