Leaves of all types, including oak leaves, make excellent mulch, helping protect your lawn as well as retaining valuable moisture. They also make great fertilizer, slowly releasing nutrients such as nitrogen as they decompose. It is a misconception that oak leaves shouldn't be used as fertilizer due to their tannins. According to the Missouri Cooperative Extension, acid is not a concern with leaf mulches because they sit on top of the soil.
Rake the oak leaves into a pile off of the grass. Place them in a container if conditions are windy.
Wait for the leaves to dry out, if necessary. If the leaves are still fairly green or excessively heavy from recent rain or snow, wait a day or two for them to dry to make them easier to mulch.
Run the oak leaves through the mulcher, collecting the resulting mulch or chopped leaves as they come out the other side of the mulcher.
Spread the mulched leaves evenly across the lawn, no more than 1/2-inch thick.
Water the lawn to dampen the leaves and keep them in place.
Spread the leaves out evenly again, as necessary, if they bunch up in piles before decomposing.