Hi Chay-Ya,

Straw is what is left from a plant after the seed has been removed. Hay, on
the other hand, is cut and dried at an earlier stage (when seed is at milky
stage rather than fully mature).

To make hay, you cut it and let it dry in the sun for several days to reduce
the moisture content so it can be stored without decomposing/rotting. This
you can store in dry conditions for several years.

Hope that helps,

James