Find mushrooms in dark areas, caves, swamps, or the Nether
Place a mushroom on dirt, podzol, mycelium, rooted dirt, or nylium
Keep the light level low enough for the mushroom to stay planted
Use bone meal on a mushroom to grow a giant mushroom
Make sure there is enough space above and around it for the giant mushroom
Harvest the giant mushroom blocks with an axe or hand
Replant mushrooms to grow more
Build a mushroom farm in a dark enclosed area
Use water streams or hoppers to collect drops
Use mycelium or podzol for easier mushroom placement and spreading