Apple iMac (21.5-inch and 27-inch, Mid 2011) - Manual (Page 11)

11 Chapter 1 Ready, Set Up, Go
Step 2: To access the Internet or a network, connect one end of an Ethernet cable
to the Ethernet port on your iMac. Connect the other end to a cable modem, a DSL
modem, or a network.
Your iMac comes with 802.11n Wi-Fi technology for wireless networking. For information
about setting up a wireless connection, choose Help from the menu bar and search
for “wi-fi.”
To use a dial-up connection, you need an external USB modem. Plug the modem into
a USB port on your iMac, and then use a phone cord to connect the modem to a
phone jack.