An Ethernet card enables a computer to access the Internet by means of an Ethernet cable. An Ethernet port is necessary to connect the cable to the computer. Ethernet cards are internal and come standard on most new computers - both laptops and desktops.
Most ultrabooks and netbooks such as the Macbook Air do not have an ethernet card port, and these devices use wireless ethernet as their only connectivity method. If using a device such as this, and the wireless network isn't working properly, please stop by the Technology Helpline to check out a USB-Ethernet adapter. This will allow you to use an ethernet cable.