- 5555 is a port you make up
- 666 is the port to which you are forwarding
- 1.2.3.4 is the IP of the target host to which you are fowarding
- hostname is the host where port 5555 will be made available
- you run this command on a third machine (e.g. your local host)
This results in hostname:5555 getting forwarded to 1.2.3.4:666