The Fist of the First Men is where the Night’s Watch set up camp during the great ranging beyond the Wall, and it becomes a major turning point when the camp is attacked and overrun by wights, with the White Walkers looming in the background.

What happened there

At the Fist, the Night’s Watch tried to fortify an old ringfort, patching gaps, setting traps, and using it as a defensive base while they searched for the wildlings.

Jon Snow ends up following Ghost, which leads him to a buried bundle containing dragonglass weapons and an old warhorn, a clue that something ancient and dangerous is happening beyond the Wall.

Why it matters

The big disaster comes later in the fight at the Fist, when the Watch is overwhelmed by wights and nearly wiped out.

That battle shows that the threat beyond the Wall is much bigger than wildlings alone, and it pushes Jon’s story into the next phase of the conflict.

In one line

So, the short version is: the Night’s Watch used the Fist as a staging ground, found ominous evidence there, and then got devastated there by the undead attack.