Not able to generate apk

If you are not able to build your project even after downloading and installing ADT properly then you must have missed Downloading Build tools from Android SDK Manager.

Open your Android SDK Manager and look for Android SDK Build-tools 



If Android SDK Buil-tools is not installed then this is what blocking you from generating apk. Install it and it and everything should work fine.  Make sure that there is no compilation issues in your resource folder.