Personal Identification Number

That, when, why?

[oxygen]

I'm just joined to Google AdSense.

* Once you have accrued $50 in combined AdSense for content and AdSense
for search earnings, we'll mail a Personal Identification Number to the
mailing address you provided. You'll need to enter this PIN into your
Account Information page before payment can be sent to you. In the
meantime, you'll still be able to show ads and Google search boxes on
your web pages, and will continue to accrue earnings.

That this?
When and how I will get my PIN?
Why Google does this?

[Rodney]

Just as the text says, your pin will be issued once your account has earned $50.

They use a PIN system to verify the publishers mailing address is valid.

Publishers have reported pin delivery times from anywhere between 10 days and several weeks, although after a month if it hasn't arrived, you can request that they reissue it.