I-600A application is in the mail!

I mailed our I-600A application on Tuesday. This is to request pre-approval from USCIS (immigration) to bring a child into the US. Now we wait to receive our appointment date to go to the local immigration office to have our biometric fingerprints done. I'm very curious to find out how biometric fingerprints are different from the regular ones! What in the world does "biometric" mean??? They must be really fancy since it costs $80 a piece just for the fingerprints. The approval form that we must receive back from them is called the I-171H. Without that little form, you don't bring any kiddos home. Needless to say, that is not a form to misplace!!!