So, in curling, like most other sports, there is an object that you, the player has possession of, in which the objective is to place that objective in a specified location. The object and location are largely what varies from sport to sport, as well as the mechanism for transporting this object. For example, Soccer (football) has a sphere, which can only be kicked, and should go into a net. By other example, curling has a stone, which may only be pushed behind a certain line on the ice, and then should come to rest closest to the center of the house on the other side of the ice.
Like baseball or basketball, curling measures "shot percentage". This is the percentage of the time the player "makes their shot". Now curling isn't as definitive as say, a baseball player earning a base, or a basketball player making a shot. It's more... subjective. When the skip called for a stone to be "a guard", how do you measure that?
For example, lets look at the 1998 Winter Olympics Gold match between Sweden and Canada:
Switzerland 9 Canada 3
D. Perren: 89%
D. Mueller: 86%
P. Loertscher: 72%
P. Huerlimann: 78%
G. Karrys: 98%
C. Mitchell: 73%
R. Hart: 58%
M. Harris: 25%
So, Sweden won over Canada. And looking at the shot percentages, it's pretty apparent why this happened. Strategy counts for a big portion of curling, like any sport. However, if you can't make the shots, strategy goes right out the window. In fact, with the Canadian Skip making only 25% of his shots, this game was pretty much a blowout. Maybe the Skip and Lead should have switched spots. :)
For more information on how the shot percentages are calculated, check out: