All lawn mowers will come with a type of speed control called a throttle control lever. This lever, which is essentially a plastic slider on the handlebar, will be attached to the engine throttle via a cable hook up. As you move the slider back and forth, the cable mechanically relays these exact same movements to the engine throttle which opens or closes the carburetor, allowing either a little gas into the motor, making it run slower, or a lot of gas which will make it run faster. And this is all done with a throttle control slider.
Start your lawn mower. This is where you will first use the throttle control slider. Push the slider on the handlebar all the way forward. This action will engage the choke which will allow easy cold starting.
Pull all the way back on the throttle controller once the motor is running. This will make the engine idle. Most slide controls have some sort of visual aid icon printed on them to signify the position where the throttle control would be positioned for a slow running engine-usually pictured as a turtle-and where it would be positioned for a fast running engine-usually pictured as a rabbit. So pulling all the way back on the throttle control would line up the turtle with the lever and therefore, a motor running at idle..
Slowly advance the throttle controller. As it slides forward, you will hear the motor begin to pick up speed, and when you get to the end of the slide, the motor will be running at full tilt. This is where you want to begin cutting grass.
When finished cutting grass, pull the throttle control all the way back to the idle position, and turn off the lawn mower.