Enable Developer options within Settings on your phone. The Developer options screen might be located or named differently by phone manufacturers. This link may be useful.
Generally:
○ Navigating to Settings → About phone → Build number
○ Tapping the Build Number option seven times until you see the message "You are now a developer!" This enables Developer options on your device
○ Go to Settings → System → Developer options
○ Under Developer options enable USB debugging
Connect your phone to your computer via USB cable.
○ If device shows "Charging this device via USB" → tap for more options and set to "File Transfer"
Click here to download SDK Platform-Tools to your computer, which includes the Android Debug Bridge (ADB) application.
Extract the downloaded file into a folder and open your terminal / command prompt.
Within Terminal / Command prompt:
○ Change your working directory to the platform-tools directory you just extracted the tools to.
○ Type ./adb devices (adb devices on Windows) and press the Enter key.
§ If the result within Terminal lists your phone as "Unauthorized" your phone is likely prompting you to allow USB debugging. Tap Allow and retry this step so that your phone is listed as "device" within Terminal.
○ Input the following command in your Terminal and press the Enter key: