Let's use a non-techy example. I speak English (your home network for this analogy), and I'm trying to converse with a person who speaks Chinese (the wider internet). Neither of us understands the other's language, leading me to find someone who speaks both to interpret (the modem). The interpreter listens to what I have to say and then repeats it to the other party in Chinese. The Chinese person gives a response, which the interpreter repeats back to me in English.
Let's use a non-techy example. I speak English (your home network for this analogy), and I'm trying to converse with a person who speaks Chinese (the wider internet). Neither of us understands the other's language, leading me to find someone who speaks both to interpret (the modem). The interpreter listens to what I have to say and then repeats it to the other party in Chinese. The Chinese person gives a response, which the interpreter repeats back to me in English.