Date trees differ from a lot of fruit trees, in that it takes two different types of trees in order to produce fruit. In most fruit trees the same tree will produce both the flower and the pollen, and will be able to produce the fruit. However in date trees, pollen is collected from the male trees and is later used to pollinate the female trees, which are the trees that produce the dates. Male trees=pollen, female trees=dates. In nature pollination is accomplished by the wind but this process isn't that effective, and will only produce a few pounds of dates per tree where as a cultivated tree that is purposefully pollinated can produce a yield of hundreds of pounds of dates.
Once the pollen is collected it needs to be allowed to dry, if the pollen is stored with moisture mold may form, and the pollen will lose viability very quickly. However if pollen is properly dried, and stored in a cool environment such as a refrigerator the pollen can keep its viability until the following year.