Hi @GaimZz,
the docs are a little bit outdated on this point, it depends whether you plan to use Composer to manage your classes or not.
If you don't, it's almost impossible to declare and/or use the PrestaShop 1.7 services in your module.
If you do... well, we don't have docs "yet" to help you, but you can take a look at this module: https://github.com/friends-of-prestashop/masterclass
Hope it helps,
Edit: some docs here => https://devdocs.prestashop.com/1.7/modules/concepts/controllers/admin-controllers/#example-using-psr-4-namespacing
Mickaël