The application permissions in short are separated to two type:
1) system permissions
2) user permissions
* the system permissions, allows the application to access and use some of phone device features such as receive boot completed, battery stats and more.
All those permissions are granted by default after requesting by application
* the user permissions in short are separated to two types
1) normal permissions
2) dangerous permissions
The user permissions, allows the application to access the user's data such as access fine location (dangerous permission), access internet (normal permissions) and more.

In your phone settings, you can see the user permissions only, the dangerous permissions shown as groups with a ON/OFF option, and normal permissions usually shown as a pointed list without a ON/OFF option.

The group permissions such as:
1) group named "location" contains some permissions
a) access fine location
b) access background location
c) access coarse location
2) group named "storage" contains some permissions
a) read external storage
b) write external storage

This application, allows you to see all types of applications ( there is so many system applications installed on your phone and most of them are hidden ), by clicking on a specific application, this application will show you all requested permissions by the selected application, and by clicking on a specific permission, we will show you the permission description with its protection level