They absorb their food from dead organic matter, or other living organisms. The source of their food is called a substrate if it is dead, and a host if it is living. Hyphae absorb nutrients from the substrate, spread, grow, and produce fruiting bodies. The fruiting body of the fungus is the part that we can see, and touch.
Symbiotic partnerships occur only between living organisms.
Symbiotic partnerships are formed in three ways. A parasitic relationship benefits the fungus but harms the host. In mutual symbiosis, both fungus and host benefit from their partnership. A neutral symbiosis benefits the fungus with no harm or benefit to the host. In ectomycorrhizal symbiosis, the hyphal threads coat the tips of tree roots.