Exactly how acupressure works is still a mystery to me. Maybe I'd have to grasp the deeper workings of chinese medicine to understand it...ehem, and that's not likely to happen any time soon...
But it works. It's as easy as this picture, grasping the flesh between thumb and index finger/hand, push and hold for as long as you can muster. This point is one of the classic pain-relief acupressure points. Yes it hurts, maybe because it releases endorphins, maybe because it does something "magic" to your energy, whatever it is, it works.
There are lots of other good acupressure points you can use too, find the points in your face/temples/neck that are sore, push gently, hold and release. It's that simple:)
(If this has good effect on you, you may want to check out this book on trigger point self therapy for pain management)