Straw is the dried stalks of tall grasses like wheat, millet or barley. After people harvested the seeds of these grasses for food, they used the straw for everything from shoes to mattresses to baskets.
People have been making straw into baskets, hats and other things since at least 10,000 BC. People used straw to make useful things all over the world, from Northern Europe to China and all over North America and South America too. Straw was cheap and there was plenty of it, and anyone could make things out of it without any special tools.
You could just use the straw loose in heaps for animals or people to sleep on. Straw was softer than the ground to sleep on, and warmer. Also, when the straw got dirty you could rake it out of the house or barn and replace it with fresh straw. Schoolchildren also sat on straw bales, or just heaps of straw, on the ground.
If you braided stalks of straw together into cords, you could use them to weave baskets or shoes or hats, or mats to walk on or sleep on. People used bunches of straw, or straw pads, to scrub their floors, or to clean pots and pans.
A Korean weaver making a basket from straw
People also mixed straw with plaster to make stronger plaster for the walls of their houses, and they mixed straw with clay to make bricks for mudbrick or baked brick buildings. Finally, they used straw to make thatched roofs for their houses as well.