Help with port forwarding to an internal NAS device?

On my internal home nat'ed network (192.168.x.x) I have a NAS device
with address .111. I would like to allow access to that device from
remote sites (of course with proper restrictions and security).

I have only ONE public IP for my router, therefore I assume I must use
a "port" which would be forwarded to the directed device (i.e.:
11.22.33.44:50000 -> 192.168.x.111).

Any I understanding this correctly? If so can anyone please explain
in a little more detail how this process works?

Thanks in advance.

B