The fungal organism which produces the mushrooms you encounter on your lawn or in the forest is called a mycelium . There, hidden, it secretes enzymes to digest organic matter, and the hyphal cells absorb nutrients through their cell walls. If a mycelium thrives, eventually it will have enough energy to reproduce.
Many fungi decompose dead organic matter such as leaves, wood, feces, etc.
No other organisms can efficiently do this. Fungi cause most diseases of insects, as well as many diseases of trees and other plants. Some fungi have evolved to take advantage of multiple food sources. Instead of seeds, fungi produce spores . Most mushrooms are Basidiomycetes .