ssh is a Unix command used for remotely connecting to other servers using SSH protocol.
The simplest use is to invoke ssh command with a single parameter which is a remote server's hostname or IP address:
greys@maverick:~ $ ssh vps1.unixtutorial.org Last login: Fri Oct 5 11:59:37 2018 from 184.108.40.206 greys@vps1:~$
Default port for SSH service is 22, but it's possible to change it so you may have to specify it as an option for the ssh command:
greys@maverick:~ $ ssh -p 212 s3 Last login: Thu Oct 4 13:41:11 2018 from 220.127.116.11 CentOS Linux release 7.2.1511 (Core) [greys@s3 ~]$