Start building Android Apps

How to start creating Android Apps? How to improve mobile development skills? Which courses to take? Which websites to read? Luckily, nowadays internet is full of information. Sadly, only a fraction of it is useful. I've complied a list of some helpful resources that novice/intermediate Android developers might find useful.

• Online courses
  • Udacity: "Developing Android Apps; by Google"
    Free course with length of approx. 60 hours.
    In their words: "This course blends theory and practice to help you build great apps the right way. In this course, you'll work with instructors step-by-step to build a cloud-connected Android app, and learn best practices of mobile development, and Android development in particular".
    
  • edX: "Android App development for Beginners"
    Free course with length of 8 weeks.
    In their words: "Learn, from Google experts, the Android app development process and how to use Android Studio, as you create and develop your own apps".
    
  • Coursera: "Programming Mobile Applications for Android Handled Systems"
    Free course with length of 5 weeks.
    In their words: "This course introduces you to the design and implementation of Android applications for mobile devices. You will develop an app from scratch, assuming a basic knowledge of Java, and learn how to set up Android Studio, work with various Activities and create simple user interfaces to make your apps run smoothly".
    
  • Udemy: "The Complete Android N Developer Course"
    Paid course with 32 hours of video, 106 articles and 47 additional resources.
    In their words: "Learn Android App Development with Android 7 Nougat by building real apps including Uber, Whatsapp and Instagram!".
    
• Resources, Tutorials
  • Android Developer: Official resources from Google
    Has Design/Develop/Distribute sections.Get the SDK, browse sample code, watch stories, etc.
  • Ray Wenderlich: Android Development Tutorials
    Collection of nice tutorials with code examples.
  • Tutorials Point: Android Tutorials
    Many lessons on basics, UI, advanced concepts and useful examples.
  • Start Android: Tutorials for beginners and advanced
    Various lessons in English and Russian with plenty of useful stuff.
  • Android Arsenal: Portal with tools, libraries, and apps
    Browse useful frameworks and libraries to strengthen your development.
  • Github: Android Open Source
    Read Android OS sources, they're all open!
• News, forums, blogs
  • Android Authority: site link
    One of the largest publication dedicated to Android OS. Founded in 2007, it has more than 7 million followers.
  • Apptractor: site link
    Website in russian with interesting articles, podcasts and digests.
  • Reddit: androiddev link
    Relevant subreddit with 70k+ readers and many interesting threads.