This is an unusual choice. It was a present; I do like poetry, but I probably wouldn’t have chosen it for myself.
But it’s great. I really enjoyed it. It’s a strange story. Set in King Arthur’s round table, of course — at least at the start. The titular hero (Gawain, I mean) is said to be the noblest, bravest, most humble, etc, knight.
A mysterious, supernatural, green figure interrupts the New Year feast at Camelot and issues a challenge. Gawain takes it up, and has a year to complete his side of the deal.
He’s clearly the top procrastinator of the round table, too, because he leaves it till after the following Christmas before he sets off to find the Green Knight.
The noble hero is tested and tempted, and (spoilers) wins through. It’s short, and fun. Oddly (or not) I remember the story, but nothing of the poetry. I could go and get the book and quote you some, but I think I’ll just leave it at that.
Oh, except to say, of course, this is an ancient work, and Tolkien also did a cover version of it. But I expect you knew that.