You'll need a set of white balance cards, although it's not necessary to spend $50 on them. You can get a set for between $10 and $20 that will work just fine. I recommend the QPcard 101 calibration cards, which run about $14. If you can't afford to buy cards, you can make your own out of some matte white, gray, and black construction paper.
Mount the cards on a slate or something else that's stable. Include the cards in every shot.
To white balance the camera, get a friend or a production assistant to hold the balance cards. Zoom in on the white card until it fills as much of the frame as possible. Focus and press the "custom" balance button. Wait for the camera to balance.
Note the lighting on the wall in the example below, which is not yet balanced.
In the frame below, the lighting is balanced. Note the difference in the color of the lighting on the wall.