Find melon seeds in jungle biomes, dungeon chests, mineshaft chests, or from wandering traders
Till grass or dirt with a hoe to make farmland
Place water within 4 blocks of the farmland so it stays hydrated
Plant melon seeds on the farmland
Leave one empty block next to each planted seed for the melon to grow into
Use torches or other light sources to keep the area lit
Wait for the melon stem to mature and produce melons
Harvest the melon blocks with any tool or by hand
Replant seeds if needed to keep the farm producing
Use a hoe to keep nearby farmland from turning back into dirt
Expand the farm with multiple rows of stems and open spaces for more melons
Use bonemeal on stems to speed up growth if desired