I am new to Windows Phone app development. I want to develop a Windows Phone game and have no idea how to get started. So, I want to develop it as an app. Is it possible to develop and publish a game as an app ?
For that you just need to update your Genre in AppManifest file. See here:
Each Windows Phone app has a manifest file that contains details about the app, such as the App ID and the capabilities that the app uses. This topic defines the elements, tags, and attributes in the app manifest file. The manifest file name is WMAppManifest.xml. The file is located in the Visual Studio Solution Explorer window, in your project Properties folder, or you can find it by using Windows Explorer.
Genre
The default value is either Apps.Normal or Apps.Games depending on the project type. Apps that use Apps.Normal appear in the app list on the phone. Apps that use Apps.Games appear in the Games Hub on the phone.
http://msdn.microsoft.com/en-us/library/windowsphone/develop/ff769509(v=vs.105).aspx