Final answer:
Gawain's arrangement with the Green Knight was a game where they exchanged blows, with Gawain knowing he would receive the blow in return a year and a day later.
Step-by-step explanation:
Gawain's arrangement with the Green Knight while staying in his house was a game. The Green Knight challenged Gawain to exchange blows with him, with the understanding that whatever blow Gawain struck would be returned in a year and a day. Gawain agreed to the game, and they exchanged blows. However, the Green Knight did not strike with full force, and Gawain survived the blow. Gawain then had to journey to find the Green Knight a year and a day later to receive the blow in return.