WhatsApp E2EE How does it works?

Question

HI All, I am very curious about how WhatsApp End-2-End Encrytion does it work?

I read a lot about E2EE but how sender knows my public key.So receiver decrypt that sender's message using receiver's private key.

 

Person A -> Message + Public Key(Of person B) // Encryption

Person B -> Own Private Key + Message// Decryption

 

I am curious about highlighted part.

Please provide your solution.