From the left edge of the device, remove the card tray.
Utilize the insertion/removal tool (it comes in the box with the device) to unlock the tray by inserting it into the provided slot then remove the tray.
With the gold contacts facing down and the notch located in the lower-right, insert the SIM card into the tray as shown.
Ensure that the card is properly seated in the tray with the front of the card under the notch.
Insert the card tray.
Press in on the tray to lock it into place.