How to enable smartphone debugging mode/development option

• Enable USB debugging on your device.
• On most devices running Android 3.2 or older, you can find the option under Settings > Applications > Development.
• On Android 4.0 and newer, it's in Settings > Developer options.
  Note: On Android 4.2 and newer, Developer options is hidden by default. To make it available, go to Settings > About phone and tap Build number seven times. Return to the previous screen to find Developer options.

Android 4.2以上版本
在Build numer選項按七下以打開開發人員選項

source:

https://developer.android.com/tools/building/building-studio.html