How to create ssh tunnel and keep in running

I want to access machine A which is behind the firewall through a jump host from machine B.

I want to do the same either via ssh keys or via username and password.

What will be the steps and the commands to achieve the same?

Solution

The feature is called port forwarding:

 ssh -L localport:machine-a-address.domain:remote-port machine-b

Then you can simply use localpott on localhost to access the remote service on machine-a, for example:

telnet localhost localport