The Public and Private key pair comprise of two uniquely related cryptographic keys (basically long random numbers). The Public Key is what its name suggests - Public. It is made available to the interacting parties. On the other hand, the Private Key must remain confidential to its respective owner. Because the key pair is mathematically related, whatever is encrypted with a Public Key may only be decrypted by its corresponding Private Key and vice versa.
Public and Private key pair helps to encrypt information that ensures data is protected during transmission.