Theme and module.module file

Hello,

I tried Drupal 8, i created a module called 'book' located in sites/all/modules/book and i created a controller, form... without problem.
But when i tried to use https://www.drupal.org/docs/8/creating-custom-modules/theming, i created book.module file, i followed the documentation but my template is not rendered. Moreover it seems that my book.module is not working because i put a die('dead !'); inside and nothing appear, i got the page without template.

Did I have to declare book.module file somewhere ?
Because I put die('dead !') in another module file (webform.module file in webform module) and i saw 'dead !'

Thanks for helping ;)
@+
S.