First of all, i’ve spent many week or months in trying to configure the ML/NL converter. It’s a powerful although hugely complicated beast. The manual wasn’t overly helpful, but there were a few folks in this forum who really greatly helped. You may want to search for the main thread, which has a few pages on various configurations.
To answer your Q: you need to connect the ML/NL with your home network. It doesn’t have wifi, so you need to connect your lan with a network cable to the ML/NL. Also power of course. That’s the first step. You can see the IP in your router and then connect through it in your web interface. you could also use the beosetup up, but i found the web interface more convenient.
If you want to connect speakers to the ML/NL, use the PL. If you want to connect other ML devices to it, use the ML out.