1
Your "private key" is what you use to decrypt messages you receive.
2
It makes it pretty easy to create a PGP key pair and decrypt messages, but there are some limitations.
3
The Obama administration has decided not to pursue legislation forcing tech companies to decrypt messages for law enforcement-atleast not for now.
4
Each users' computer can still be hacked to steal his or her cryptographic key or simply read the recipients' decrypted messages.