Are you looking for game design tutorials? This app is for you 

The Game Design Toolbox is an iOS/Android app that provides high quality game design tutorials.  Each tutorial is dedicated to a specific design issue and is illustrated by examples from actual game design documents. Tutorials are grouped along five themes:

• Game concept
• Game mechanics
• Level design
• Storytelling
• tools and methods

The tutorial dedicated to the content of the game design document is free. The others cost a few Euros or $.