If you read pages like this where they teach you how to install ROMs, Rooting your terminal, install a custom recovery, etc ... sure you read several times that you must activate the "USB Debugging" mode.
Normally we explain how to do it right there quickly, but today we dig a little on the subject and explain what it is and how it works. Then also will explain how to activate in different versions of Android.
What is the "USB Debugging" mode?
The "USB Debugging" (USB Debugging) mode is primarily intended for developers. The USB Debugging mode opens direct access to the system for the Android SDK (Software Development Kit). If you download and install on your computer the Android SDK but not activate the debug mode the SDK will not work, since you can not connect to the device.
USB debugging mode is not only useful for developers, but also used it to perform other operations such as installing a custom ROM. Let's see how to enable it.
How to Enable USB debugging on Android KitKat and Jelly Bean (4.2 and later)
We will go to Settings> Phone> (we move to end)> will press several times on the number compile option and we see a message announcing that we are already a developer.
Back back and see that there has appeared a new option titled "Development Options". Enter and mark the "USB debugging" option. We will give OK to the message that appears us. And we are.
We can activate or deactivate whenever we want to repeat the same process.
How to Enable USB debugging on Android 4.1 and 4.0
We will go to Settings> Developer options and will qualify. Once enabled we will go to the USB Debugging option and activate. We'll give OK and you're done. In this case it is very fast.
How to Enable USB debugging on Android 2.3 Gingerbread and earlier
In this case it is very simple. We just head to Settings> Applications> Development> USB Debugging and activate. As simple as this.
As you can see is very simple and is a process that takes less than a minute. You can activate and deactivate your liking, depending on when you may need or not.