Fungi reproduce in a couple of different ways. Some reproduce asexually. If a few fungus cells break off and the conditions are right, a new fungus could grow. The offspring is created from a piece of the parent.
However, many fungi reproduce sexually through spores. A spore is a tiny and lightweight reproductive cell that can develop into a new living thing if it lands in the right conditions. Fungi have special structures that produce spores, and they produce a lot of spores—millions and trillions of spores. Once released by the fungus these tiny little cells can be carried miles by wind and water.
This is pretty ingenious actually. With so many spores, the chance of some landing in the "right" environment is very good, and the species will continue.
Bottom line...spores have helped fungus become a very successful kingdom!