1) Make sure you are viewing the active step count screen. Click MODE until you arrive at the clock, then click MODE one more time to view active step screen. 

2) Walk more than 15 consecutive steps to start the count on the sensor

3) Make sure your step sensor isn't paused. If you don't see a little man on the bottom left corner, the step sensor is paused. 

While the Pedometer is Paused it won't count any steps at all. To resume counting steps, hold down the MODE button on the step screen until you see the little man return on the left side of the screen.

To activate Pause mode,  you would Hold down the MODE button while on the step screen until the little man on the left of the screen disappears.