I have searched all the resources. But nothing tells how to develop game on android plarform. For example, how to display a 3D model on android. More specific, I just want to know how to export the project and generate a APK file.
Follow the guidelines for iPhone and mobile in general about keeping your assets lean. Avoid OnMouseDown. Other than that, it's the same.
You use Build Settings to set platform to Android. Player settings are pretty basic stuff. Build and Run will install it on the device and run it. If you'd rather build an APK you can transfer to another device(s), use Build instead and save the APK where you can find it. Then you can email that or post it on a FTP or HTTP web site or Bluetooth it or wifi it or USB it, whatever you like. Once on the Android, you should be able to find it with the built-in file stuff, or get Astro. Clicking on the .apk file will bring up the 'you wanna install this?' prompt, just say yes.