A mushroom is a fungus-like plant that is used as an ingredient in some crafting recipes. If the area around is dark enough, it will start to spread to nearby blocks. They can be either red or brown in color and they can only grow on podzol blocks.
Both red and brown mushrooms (via screenshot)
Mushrooms are naturally generated in poorly lit areas with light levels of less than 12, if this requirement is met red and brown mushrooms have a 12.5% and 25% chance of spawning respectively. Mushrooms can be found in swamps, old-growth taiga, mushroom fields biomes, and in the Nether. You can obtain both red and brown mushrooms by using shearing the respective mooshrooms.
A brown mushrooms in a swamp (via screenshot)
Mushrooms can be planted and grown on blocks such as mycelium, podzol, or nylium. Both variants red and brown grow at the same rate regardless of the light level. Mushrooms are used to craft items such as fermented spider eye, mushroom stew, rabbit stew, and suspicious stew.
Mushrooms have a chance to spread to nearby blocks if there are less than five mushrooms of the same type in a 9x9x3 volume around the original mushroom, this allows players to farm mushrooms.
Making mushrooms stew (via screenshot)
Mushrooms are fungus-like plants that are naturally generated in dark areas. They are used for making stews that can be consumed and fermented spider eyes that are used for brewing. They can be farmed making them a renewable plant.
A. You can find mushrooms in swamps, old-growth taiga, and in the Nether.
A. Mushrooms are used for making mushroom stew, rabbit stew, and fermented spider eyes.
A. Giant mushrooms can be grown by using bone meal on red and brown mushrooms.