First of all, the public key and private key are commonly known as asymmetric encryption, that is, asymmetric encryption algorithm, which is an improvement on the previous symmetric encryption (using user name and password).

When using asymmetric encryption algorithm, two pairs of keys will be generated, one of which is private and must be kept very carefully. It is better to add a password without transmission, so it is called private key. The private key is mainly used for decryption/signature. The other is public, for everyone to use. It doesn't need to be kept secret, so it is called a public key. The public key is mainly used for encryption/authentication. When you encrypt information with one of the keys, only the other key can be decrypted, so the public key and the private key form a unique correspondence. Based on this unique correspondence, asymmetric encryption can first be used to verify the identity of the sender of information, and the other is secure transmission.