Answer: Leaf mold is simply partially decomposed leaves. Leaves in a simple pile outdoors will eventually become leaf mold all on their own, just as they would on the ground in the forest.
In my experience, simply putting the leaves in a bag for a few months does not work at all. They will need to be dampened and, since leaves are very high in carbon, you will also need to add a source of nitrogen (such as fertilizer or fresh barnyard manure) in order for them to begin to compost. They should be stored well above freezing, because the colder the temperature the slower the process; warm temperatures are really best. Chopping the leaves will also speed things up, as will stirring the mixture from time to time.
Instead of composting the leaves, you could simply chop them and use them as mulch or as a soil amendment, digging them in lightly. They will break down over time and feed the soil that way, too.
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