Q:

How to use FIN in TCP and why?

I recently am attempting to study the TCP, but a post graduate tell me the FIN is also used in  going to create a connection, that 3 handshakes.
Following is my mind to the process of 3 handshakes:

Client A post a datagram within SYN to Client B.
Client B received it, and immediately posted another datagram within SYN and ACK.
Client A received it, and immediately posted another datagram within ACK to Client B.

When the 3rd step is DONE, the connection is going to be built.
Here is the question, I don't find any datagram with FIN in 3 steps. 

A:

FIN is not used in creating a connection. It's used to close a connection. 
However, the connection can be closed with FIN halfway through a handshake, as this diagram makes clear. Perhaps this is what the Post Grad was referring to?

