For the security of your users, your app must declare what devices and features it will use.
As an app user, I wouldn’t want to be playing a video game only to discover afterwards that the app had been taking video footage of me during the game without my permission. I also wouldn’t want to use a social media app that started accessing pictures from my library without my permission. That is why when you create an app for the store you must edit the App Manifest file and specify the capabilities of your application. This provides the user with disclosure of capabilities and libraries the app you are installing may choose to access.
The app manifest file is a XAML file, but rather than edit the XAML directly, we use the app manifest designer. To open the app manifest designer, go to Solution Explorer and double click on the file called Package.appxmanifest. We specify the features and devices our app wishes to access on the capabilities tab.
When you select a particular capability, you allow the app to request access to that feature or device.
TIP: Many of these capabilities do not need to be declared if you use the File Picker to access files on the user’s device. If you use the File Picker control then the user is directly involved in selecting the music, picture, video, or file that you are accessing so they are fully aware of the fact your app is accessing content.
Here is a summary of the different capabilities you can set. For a complete description visit the app manifest documentation on MSDN
Don’t forget when you are finished your app you can publish it and get rewards through the Developer Movement.