The default port for SSH on Linux systems is 22. There are a few reasons why you may want to change this to some other number. If multiple servers share the same IP address (behind a NAT configuration, for example) you usually can't have them running SSH on the same port and expect to access them from outside the network.
This is a companion discussion topic for the original entry at https://linuxconfig.org/how-to-change-ssh-port-on-linux