The Green Knight challenges King Arthur's brave knights to take a swing at his neck he says the favor will be repaid in a year and a day.
King Arthur you are above this, I accept your challenge, green knight!
I accept your challenge
Sir Gawain chops off The Green Knight's head, they agree to meet again a year an a day later.
Find me in a year and a day.
On his quest o find the Green Knight, Sir Gawain ends up living with a King and a Queen, he almost has an affair with the Queen and she gives him a green girdle which is meant to protect him from the Green Knight's strike to his head.
Sir Gawain arrived at the Green Knight's chapel. The Knight was sharpening his ax that would be used to chop off Sir Gawain's head.
You take too long.
I was sharpening my ax.
The Green Knight finally strikes Sir Gawain after taunting him and Sir Gawain survives because of the girdle.
The Green Knight reveals himself to be the king and tells Gawain that he did not act like a chivalrous knight because he accepted the girdle from the Queen. Sir Gawain is ashamed and feels that he is a false knight.