What is the best and least expensive way to set up a wooden swing set in an unlevel yard?

We are buying a wooden swing set from a friend, so there is no manual etc....Our backyard is not so level.|||Many wooden sets are not heavy enough to be stable during use so ideally the legs should be set in concrete, or you can drive stakes into the ground and tie or bolt the legs to the stakes. Either way you still have to dig down in the dirt for the legs on the high side of the yard until the set is level. |||do you have a tree with a big limb? is the swing got a frame? Need more info on what type swing your getting. if it has a frame perhaps you could dig till its level