What happen in the green chapel in the story of Sir Gawain and the Green Knight?

At the begining of Sir Gawain and the Green Knight the Green Knight arrives at Camelot sometime between Christmas and the New Year and asks to play a beheading game with the knights there. The Green Knight will kneel and offer his neck for a single blow to one of the knights at Camelot, then one year later the champion must come to the Green Knight's chapel and return the favour.

The knights at Camelot don't like the sound of this. But Arthur (who is described as child3ered - probably childish) accepts the challenge. Arthur's best knight - Gawain - explains that Camelot cannot risk its king on such a silly game, and accepts the challenge himself.

Gawain beheads the Green Knight at a single stroke. The Green Knight picks up his head, reminds Gawain that he has an appointment at the green chapel for a year from today, then leaves the hall.

....

Most of the poem covers Gawain's trip to the Green Chapel to keep his assignation. On his way there Gawain is three times tempted by a mysterious woman who is the wife of a knight who offers him shelter in his castle. Gawain flatly resists the first two temptations, but at the third asking agrees to wear a talisman which will protect him from the Green Knight's stroke.

....

At the Green Chapel Gawain offers his neck. The Green Knight fumbles the first two attempts, but at the third lightly nicks the back of Gawain's neck. Gawain jumps up ready to make a fight of it.

The Knight now explains that this has all been a test of valour. Gawain resisted the first two temptations, so the first two strikes missed. The third temptation Gawain partly succumbed to, so he got grazed (but not killed).