Question
You want to know discretely what the second way of the three-way handshake is in the context of TCP/IP networking. What is it?
Short Answer
It is the sending of a TCP packet with a flag of "SYN-ACK" from the server/destination to the initiating client (after the first way was completed).
Longer Answer
The second way is sending a TCP packet with the "SYN-ACK" flag (of which several potential flags are possible) to the destination:
Server -----> Client (initiating machine)
TCP is used in HTTP communications. TCP uses a three-way handshake; each way has a specific flag in a TCP packet and a specific source and destination (among the two end point devices involved). When a workstation tries to connect to a website (e.g., https://www.continualintegration.com), the workstation sends a TCP packet with a SYN flag to www.continualintegration.com. Then the server sends a SYN-ACK to the client, and this is the second way.
To read more, see these postings:
https://ddos-guard.net/en/terminology/protocols/tcp-3-way-handshake
https://www.techopedia.com/definition/10339/three-way-handshake
What Is The First Way of the Three-Way Handshake?
What Is The Third Way of the Three-Way Handshake?