The Airport base stations act as WiFi router in the network. There are two different models which differ in terms of performance (range) and the number of connections.
Description of the Ports:
USB-Port: Not used in our setup
LAN-Ports: Used to connect the printers and other network devices
WAN-Port: Connects the device with the internet. Your internet router is connected to this port.
Important: If you are using multiple Airports, they will be connected to each other via the WAN connection.