Can someone help me

clarify these instructions: Dec 1 st at neck edge every 4th row 6 times, every 6th row 13 times, At the same time.

Those Words “At the same time” will be refering to whatever instructions follow them. not those before them.
you are shaping the neck, [B]as well as[/B], ‘at the same time’ , perhaps shaping armholes or some other pattern detail.