This tutorial seeks to teach you how to farm seagrass, which are plants that are naturally found underwater.
Seagrass spontaneously generates by applying bonemeal underwater. Applying bonemeal to seagrass will cause it to increase in height, similar to normal grass. This bonemeal can be applied by a dispenser, but the seagrass is only obtained upon the player breaking it with shears.
Seagrass is easily farmed by simply applying bonemeal to an underwater surface and then AFK-left clicking with shears. New shears can be given to the player as they break, allowing for continuous farming.