Test your skill against the computer. It's not an easy task. You've got six missions in which to match wits with the computer for a higher score. Each time the bricks in the canyon are hit, the remaining bricks "fall" to a lower level (rather than remaining stationary in their original position). Bricks that fall to a lower level are worth the points designated for that level.
Keep an eye on the solid bar beneath your score on the upper right side of the screen. It is a "miss indicator" and gradually decreases in length each time you miss until six misses are recorded and the game ends. The bar is also color-coordinated with your planes and your score.
--From the Atari 2600 Canyon Bomber instruction manual.