Instructions
Insert fresh batteries into your wireless controller. The controller comes with a battery pack that fits into it (which takes two AA batteries). You can also use the separately sold, rechargeable battery pack.
Turn on the Xbox 360 console using its power button. Press and hold down on the wireless controller's "start" button--the center white button with the green X--to turn the controller on.
Press the small "connect" button on the console, which is located near the disc drive. If you have the console standing vertically, the button should be near the bottom and to the left of the drive.
Push the controller's "connect" button, which is located on the back end of the controller, near the spot where the cable would come out of a wired controller.
Look for the rings of lights surrounding both the console's and controller's power buttons to flash in a spinning circle. The top-left-hand light quadrant on both devices should then flash. This indicates that the controller is now programmed as the console's "number one" controller.
Repeat the above steps for any more wireless controllers you are programming to the console. For each controller you program, the next light quadrant on the console should light up: top right for number two, bottom right for number three, and bottom left for number four.