At their core, fungi are networks. If you look at images of a developing human, you would see a single cell reproducing, becoming a ball of cells, then a hollow ball of cells, then eventual differentiation with an opening in the ball and orientation developing, through stages of development, getting closer and closer to something that we would recognize as a human.
If you look at a developing fungus, what you'll see is an expanding network of threads. As those threads expand, they're sensing the environment, exuding enzymes to break down the material that they are spreading in or on so they can absorb nutrients to fuel more expansion. If they find something they like, they'll expand their network in that area, adding hyphae and making a thicker mass of fibers, like a larger rope that is still made up of strands, just more of them.
One of the reasons that this is important to us is that these threads can also form networks with plant roots (mycorrhizal relationships) so that the fungus can barter with plants. The fungus has it's tiny hyphal "fingers" all through the soil, so they are very good at accessing nutrients, while the plants are busy above-ground using the energy from sunlight to turn carbon dioxide and water into sugars, something the fungi just can't do. So they can share back and forth, nutrients for energy, a win-win.
These relationships are so important that nearly all land plants depend on them, and in most cases there are several fungi associating with each plant and several plants with each fungus, forming what has been referred to as the "wood-wide-web," a term coined in 1997 in an article in the journal Nature by lead author Suzanne Simard and her co-authors. For more on these relationships, here is a link to a very informative review article in Tansley Reviews.