The ways to enable USB Debugging mode, which is accounted for the key step in Android rooting process, vary from one Android version to another. USB Debugging is required by adb, which is used for rooting, backing up, installing a custom ROM, tacking screenshots from computer and more

[tpb]1. Android 2.0-2.3.x[/tpb]

[tpb]Settings > Applications > Development > USB Debugging.[/tpb]

[tpb]2. Android 3.0- 4.1.x[/tpb]

[tpb]Settings > Developer Options > USB Debugging.[/tpb]

[tpb]3. Android 4.2.x and higher.[/tpb]

In Android 4.2 and higher versions, the Developer Options menu and USB Debugging option have been hidden. In former 4.X versions of Android, USB Debugging option is under Developer Options menu.

[tpb]First, you need to enable "Developer Options Menu".[/tpb]
1. Click Menu button to enter into App drawer.
2. Go to "Settings".
3. Scroll down to the bottom and tap "About phone" or "About tablet",
4. Scroll down to the bottom of the "About phone" and locate the "Build Number" field.
5. Tap the Build number field seven times to enable Developer Options. Tap a few times and you'll see a countdown that reads "You are now 3 steps away from being a developer."
6. When you are done, you'll see the message "You are now a developer!".
7. Tap the Back button and you’ll see the Developer options menu under System on your Settings screen.
[tpb]Now, you can enable USB Debugging mode.[/tpb]
8. Go to Settings>Developer Options>USB Debugging. Tap the USB Debugging checkbox.


[tpb]4. Android 5.0 Lollipop[/tpb]

To enable USB Debugging on Android 5.0 Lollipop is the same as Android 4.2.x.

Settings > About Phone > Build number > Tap it 7 times to become developer;
[tpb]Settings > Developer Options > USB Debugging.[/tpb]

[tpb]NOTE: USB Debugging should only be enabled when you need it. Leaving it enabled all the time is kind of a security risk for that this mode grants you high-level access to your device. Say if you connect your Android phone to a USB charging port in a public location, the port could use the USB access to your phone to access data on your phone or install malware. This could happen when and only when USB debugging mode is enabled.[/tpb]