How does the sender find out the ip-address and port of the recipient?

Question

Communication protocols

I am trying to figure out how the Internet works and I have a question that is not clear in the information resources.
The computer the sender sends a request to transfer such and such information to such and such a computer, application on port n, and the recipient must make sure that it was the sender who sent him the information and not another computer
There was such a question as initially the sender knows the ip-address and port of the recipient and how the recipient knows the ip-address of the sender

Answer 1

There was such a question as initially the sender knows the id-address and port of the recipient and how the recipient knows the id-address of the sender

Well, firstly, this topic only works on protocols with authentication and authorization (google AH and ESP). You can also google "public and private key", that's just it.
Secondly, if without encryption, then the TCP packet just has the address and port of the sender, to which the recipient sends the response.