Google AdSense send you a PIN (Personal Identification Number) to verify your address, after you earned 10 US $ at your AdSense account.
How to do PIN verification : Google AdSense
Step 1 – Sign in to your AdSense account at www.google.com/adsense/ with the email id and password of your AdSense account.
Step 2- Click on gear icon (settings) on left navigation bar.
Step 3- Click Account Information, then click Verify Address.
Step 4- Enter Your PIN. (its a 6 digit number you get via speed post at your address). click on Submit PIN.