I need to know what is public key infastructure. I need to know is this related to sending requests and response as like WsHttpbinding in WCF.
There is no direct relation between a PKI and a WCF service. PKI is the infrastructure for creating and managing digital certificates that among many other purposes can be used to encrypt the data flowing through a WCF service.
Once you have a private key and a digital certificate to distribute its coresponding public key you can "forget" about the PKI behind it (in most cases).
If you need further information on how to actually use the certificates to secure your WCF, let me know.