The .p12 contains both the private and the public key, and also information about the owner (name, email address, etc. ) all being certified by a third party. With such certificate, a user can identify himself and authenticate himself to any organization trusting the third party.
You should be able to see the content of the p12 file with
openssl pkcs12 -info -in filename.p12
provided openssl is installed in your system.