In a Gas Powered lawnmower How does the Spark Plug keep sparking after Engine Started?

Maybe i dont understand how spark plug works but from what i gather, spark plugs are the spark that starts the combustion process in the engine...So when i pull the cord on my lawnmower it essentially creates electricty to start that "FIRST" spark by the spark plug starting the combustion...What i dont get is how the Spark Plug continues to "spark" and keep the engine running after my first cord pull?