laravel backpack "not understanding about user login role and permissions"

Hello, i am analyzing laravel backpack trial package, i am not sure about user role and permission.

I am seeing in database model_has_roles table

    role_id         model_type           model_id

      1         App\Models\BackpackUser    3
      2         App\Models\BackpackUser    4

and model_has_permissions table

    permission_id     model_type           model_id

      1            App\Models\BackpackUser     3
      2            App\Models\BackpackUser     4

i want to ask that what is model and how it is work?

via Chebli Mohamed