Wireless internet help?

So i'm totally computer illiterate and have no idea what im talking about, but im hoping you can help. I have an airport and this other black thing. Is the airport the modem and the black thing the router? i dont no (sorry this is so vague i don't know anything about computers). But everything appears to be connected that should be, although a cable might be missing i'm really not sure. Can you tell me why it isn't working? If you need more info maybe i can go and check it out and see if there is a specific cable missing or something. Help please!