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What is USB Debugging Mode?If you use an Android phone and you’ve searched forums for solutions to problems, you’ve probably heard the term “USB Debugging” every once in a while. You may even have seen it while looking through your phone’s settings. It sounds like a high-tech option, but it really isn’t; it’s quite simple and useful.
USB Debugging Mode is one thing that you cannot skip to know if you are an Android user. The primary function of this mode is to facilitate a connection between an Android device and a computer with Android SDK (Software Development Kit). So it can be enabled in Android after connecting the device directly to a computer via USB.
Why I need to enable USB Debugging Mode?USB Debugging grants you a level of access to your device. This level of
access is important when you need system-level clearance, such as when
coding a new app. It also gives you much more freedom of control over
your device. For example, with Android SDK, you gain direct access to
your phone through your computer and that allows you to do things or run
terminal commands with ADB. These terminal commands can help you
restore a bricked phone. You are also able to use some third-party tools
to better manage your phone (for example, Syncios Mobile Transfer [syncios.com]). So this mode is a useful tool for any adventurous Android owner. 
Now, please follow these steps to debug your Samsung Galaxy Note 9.
Step 1 : Turn on your Samsung Galaxy Note 9.
Step 2 : Go to your Samsung Galaxy Note 9 “Application” icon and Open Settings option.
Step 3: Under Settings option, select About phone, then choose Software Information.
Step 4: Scroll down the screen and tap Build number several times until you see a message that says “Developer mode has been enabled”.
 

 
Step 5: Select on the Back button and you will see the Developer options menu under Settings, and select Developer options.
Step 6: Slide the “Developer Options” button to “On” and turn on “USB debugging”.
Step 7: You will see a messages “Allow USB Debugging”, click “OK”.