App Permissions are Divided into two categories: General Use Capabiltiy and Special Use Capability.
General Use Capability
Provides programmatic access to files on removable storage, such as USB keys and external hard drives, filtered to the file type associations of the app.
Access to the microphone’s audio feed, which allows the app to record audio from connected microphones.
Access to the webcam’s video feed, which allows the app to capture snapshots and movies from a connected webcam. Only grants access to the video stream excluding Audio stream.
Access to location functionality, which you get from dedicated hardware like a GPS sensor in the PC or is derived from available network info.
Enables multiple devices in close proximity to communicate with one another. This capability is typically used in casual multi-player games and in apps that exchange information. Devices attempt to use the communication technology that provides the best possible connection, including Bluetooth, WiFi, and the internet. This capability is used only to initiate communication between the devices.
Internet and public networks:
Outbound access to the Internet and public networks through the firewall. Almost all web apps use this capability.
Home and work networks:
Inbound and outbound access to home and work networks through the firewall. This capability is typically used for games that communicate across the local area network (LAN), and for apps that share data across a variety of local devices.
Access to your music library and playlists, including the capability to add, change, or delete files. This capability also includes music libraries and playlists in the music library on HomeGroup computers, plus music file types on locally connected media servers.
Access to your pictures library, including the capability to add, change, or delete files. This capability also includes pictures libraries on HomeGroup computers, along with picture file types on locally connected media servers.
Access to your videos library, including the capability to add, change, or delete files. This capability also includes videos libraries on HomeGroup computers, along with video file types on locally connected media servers.
Special Use Capabiltiy
Special use capabilities are intended for very specific scenarios.
Typically used in line-of-business apps that connect to servers within an enterprise. Windows domain credentials enable a user to log into remote resources using their credentials, and act as if a user provided their user name and password.
Shared User Certificates:
Access software and hardware certificates, such as certificates stored on a smart card.
Access to the user's Documents library, filtered to the file type associations declared in the package manifest.
Detailed Explanation on MSDN