When you open the front door of the serger (where the lower loopers are threaded) on the right side of the section there is a lever with a picture that shows stretch or gather...I think gather is down...without the machine in front of me, I don't remember too well. No special threading or special needles...just moving the lever. It doesn't really gather, mostly for easing the fabric ...
You have purchased a real gem...she is a nice heavy duty serger. Wish they made them like that today....