ssh is a Unix command used for remotely connecting to other servers using SSH protocol. ssh is sometimes called the ssh client component, while sshd is the server component of SSH software.
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 22.214.171.124 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 126.96.36.199 CentOS Linux release 7.2.1511 (Core) [greys@s3 ~]$