A part is missing that sits on top of the vent, looks like it broke off or something. The cylindrical thing to the right of the vent in 2nd pic has a horizontally-acting striker, cocked by pulling to right. The sear shaft is vertical and is pulled up by the lever with brass handle, when brass handle is pushed downward.. That releases the strriker which then impacts some kind of cap or primer in the missing piece. The missing piece communicates the flame to the vent. Bang!