After you begin developing your app, you may have more specific questions. To answer those I really recommend
StackOverflow. Likely the question will already be answered there. If not, then it is easy to ask one, and the community there is very helpful.
To learn how to make apps for Windows Phone, I just started making one. When I ran into problems, I searched for articles, tutorials, ect to fix them, and continued. After that first app, creating future ones became much easier.
I hope this helps you!