That little chain hanging from your bbq is a matchstick holder for lighting the grill manually when the electric igniter system is broken.
To light your grill with the matchstick holder, place a match in the holder and then strike it to light it. Then turn on one burger. Then depending on where the match holder is placed you will either poke the lit match through the grill grate or place it through an access hole on the side of the grill.
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