relations() in Yii, do not understand the example from the book

relations() in Yii, do not understand the example from the book

I read a book Pactpub Web Application Development with Yii and PHP Nov
2012. Faced with such a problem, I can not understand the logic behind the
use of relations (). Here diagram tables in the database:
You need to insert code in the model:
Issue model:
...
'requester' => array(self::BELONGS_TO, 'User', 'requester_id'),
'owner' => array(self::BELONGS_TO, 'User', 'owner_id'),
'project' => array(self::BELONGS_TO, 'Project', 'project_id'),
);
...
Project model:
...
'issues' => array(self::HAS_MANY, 'Issue', 'project_id'),
'users' => array(self::MANY_MANY, 'User',
'tbl_project_user_assignment(project_id, user_id)'),
...
I can not understand that we add? If the model Issue understand
everything, then the model Project - I do not understand that we are
adding. Help to understand ...