Oak leaves are actually the fall season's gift to the composter. The mineral rich organic matter that trees shed to give us an all natural effective mulch in the winter and, once decomposed, extremely benefit to the soil. Shredding of the leaves adds to their decomposition and grass clippings mixed in adds nitrogen to help in the process of breaking the leaves down.  Leaves by themselves do not make the rich soil but they make leaf mold, a great soil addition. Leaf mold is a step past leaf mulch, leaves left in contact with the earth and its all natural microbes will slowly turn to leaf mold. Leaves vary in the amount of acidity that they add to the soil. Make sure to test your soil for the proper Ph before planting and add lime or other alkaline substances to make it correct. Leaves contain twice the mineral content of manure. Being they are a form of organic roughage, they improve drainage and aeration of the soil. Leaves provide nutrition for beneficial microbes making the soil come alive and thrive. An efficient way is to put all of the shredded leaves directly on the garden add a little chicken shit will help the carbon to nitrogen balance. Yeaaa to the chickens..the leaves could also be covered which conserves heat and moisture but they should be uncovered and turned to reduce matting of the leaves..in the spring it will all be a part of the soil, nutrient rich ,and ready for planting.