Activating Developer options and enabling USB debugging in Android Marshmallow:
In the new version of android(Marshmallow) “Developer options” are disabled by default because not every Android user is a programmer or a geek therefore Android kept “Developer options” disabled in all Android powered devices. In Android Marshmallow they have made a few changes to the settings page for activating developer options and this quick tutorial will help you activating developer options and enabling USB debugging.
Go to settings in your android device and click on “About device” option.
Select “Software info” from the about device page.
Now tap 8 times on the “Build number”, this will activate developer options.
Now go back to the setting page and scroll down until you see “Developer options”. Select Developer options.
On Developer options page scroll down and enable USB debugging.
This is all for enabling USB debugging on Android version 6.0.1 (Marshmallow), pretty simple. Do ask in comments for any difficulties you face regarding to android.