Describe the event surrounding Buck's Moccasins. what finally became of them,why?

Buck is not initially toughened up in the Yukon's cold and snow.  His feet cannot take the work of being a sled dog until they become less tender.  The men make his moccasins so that he can continue to help pull the sled while he becomes more accustomed to the natural environment.

In the end, Buck's booties get worn out and unusable, but by that time Buck has now got a "Tougher" paw to walk on in the weather of winter in the Klondike.