The private key is kept by itself and the public key is made public. Because the private key is unique and only known to itself, it can be used as an identity, so it can be used to sign.

When 1.PGP generates an account, it will generate a secring-bak (private key) and a pubring-bak (public key) in my document. The private key file is 2K when exporting and 4K when including, which can be viewed with Notepad.

2. Someone else's public key must be given to you. If you encrypt it with your own public key, others will not see it.

3. If the export key selection does not contain a private key (it is not selected by default), it is a public key, which can be opened and viewed by the key size or text.

4. There is no public key encryption and no private key encryption. Anyone who uses public key encryption can decrypt it.