c2-c5

I have an expired Green Card and have a few questions on the process of
filing the I-90 for renewal. I have called USCIS Customer Service, and
they were able to answer some questions, but I still have a few, and
was hoping to get some further info.

1. USCIS Customer Service informed me that I can go to my local office
to get a 1-year extension sticker on the back of my current expired
green card as soon as I receive a notice of receipt from USCIS
indicating that they have received my I-90 form. According towhat I've
read on their website, there is nothing that precludes me from filing
the I-90 electronically. Can anyone tell me whether they've filed
their I-90 electronically and how long it takes to receive the notice
from USCIS that they have officially received the filing?

2. (This is more of a curiosity thing.) I understand that USCIS
requires an appointment for something called biometrics. When I did
the application for my original green card, the only thing that was
required was a set of fingerprints, which I was able to get at my local
police station. Can someone tell me what is meant by biometrics and
what the general biometrics process entails?

Thanks in advance for your time and advice.

C.