Hemp is a plant that is added to the world generation, it can be farmed. Hemp is used to create canvas.
Hemp is generated in the world just like sugar cane, meaning: next to a water source on a grass or sand block. Hence hemp can easily be found in a spawn biome, this does not imply that hemp can't be found in other biomes, it can be found anywhere next to water, for example in the image below it is spawned in a forest.
Hemp can be generated in any of its growth stages. Be careful, a hemp plant will only drop hemp if the plant is broken in it's fourth or fifth grow stage!
When planted it will first grow like wheat as a crop, when broken in this stage notting will be dropped. After some time the plant will be in it's fourth grow stage, now when broken one hemp will drop. To gain more hemp you need to wait till the plant reaches it fifth growed stage, in this stage the hemp will expand in height to two blocks, this is also the final grow stage.
Now one can chose if they harvest the complete hemp for two hemp items or only the top. When only the top is broken one hemp will drop and the plant will be reverted back to it's forth grow stage, then after some time it will again grow to a two block tall hemp plant. It cycle can be repeated for hemp farming.
Hemp can also be grown with bonemeal.