SSH has a client/server type of architecture, similar to other TCP/IP protocols. SSH server allows multiple client connections to it. OpenSSH porting for Windows runs as a Service in Windows or a Daemon in Unix/Linux Operating Systems. The default TCP port on which an SSH service/daemon runs is 22. However, you can make SSH server listen to any port while configuring it.
SSH client is the program, which a User use to login to SSH server from a Client computer. To login to SSH server, SSH client program must need to know the IP address of SSH server, the TCP port on which the server is listening (default is TCP port 22). The Operating System user login id and related password is also required, to work at Operating System console level.