Goal : let you access to a private port, example a database listening on 127.0.0.1 only on the remote server
SSH -L <choose a localport on your laptop>:<destinationip>:<destinationport> me@myserver
Example with the database:
ssh -L 50000:127.0.0.1:5432 me@server
or with a remote database
ssh -L 50000:123.254.99.21:3306 me@server
