The girl lays on her back with her legs spread, the guy sits between them.
The guy crosses his wrists and places the backs of his hands together. he then slips both of his index fingers into her and massages the side (the walls) of her vagina. When she is relaxed enough insert the index and ring fingers (4 fingers now). The more you do this the more fingers you can get in . I have been able to get all eight into my wife but it was too uncomfortable to sustain.
This technique produces some pretty intense feelings for the woman, the three or for I have done this to have all said that they have never felt anything like it. And the guy can actually feel the striations of the vaginla muscles, which is kind of cool.
The other bonus of this technique is that it realaxes the vagina, this has two bebefits: 1. It allows deeper finger penetration making it easier to find the g-spot and 2. the womans relaxed state increases her ability to have a manual g-spot orgasm!