Before we look into private key and public key in Bitcoin network, two encryption systems should be distinguished.
Symmetric and Asymmetric Encryption
The traditional encryption system consists of only one key. It uses the same key for enciphering and deciphering the message to be transmitted. In other words you need to share your password with the parties concerned, for example your safe deposit box is so familiar with your passwords.
For asymmetric encryption, the recipient generates two keys together, a public encryption key and a private decryption key. The message is encrypted with the public key, and can only be decrypted with the private key. To conclude a pair of keys will be involved in encryption and decryption. Most likely each pair is prime numbers and interrelated mathematically.
Private key and Public key
As what the names suggest, public key is the one open to the public and everyone can read about, while private key is the one you should keep to yourself.
When Bob wants to send some sensitive message to Lisa, he would encrypt the message into a public key. No one but Lisa who owns the private key can decrypt the wrapped information.
In Bitcoin’s case, the address for each transaction is based on public key, while private key is stored in the wallet files. Through public keys, people
Thus it is agreed that bitcoin-users should keep the wallet with due care. Otherwise due to the decentralization and anonymous features of Bitcoin, no one can track your lost private keys, and the lost bitcoins under that address.