Roll the ball down the bowling alley by holding the left mouse button while sliding your mouse forward as though you were throwing the ball, and then letting go of the mouse button to propel the ball. Fast movements lead to faster and more powerful rolls. You can also adjust the ball's direction even after you've released it by clicking your mouse along the alley. This option makes Club 300 Bowling rather unrealistic, but no one's complained yet. If you think that makes it too easy, you can always not do it.
Play Club 300 Bowling!