Substances are forms of matter that have a specific composition and distinct properties. They can be classified into two main categories: elements and compounds. An element, like oxygen, consists of only one type of atom, while a compound, such as water, is made up of two or more different types of atoms bonded together. Substances can exist in different states, including solids, liquids, and gases. For example, ice is the solid form of water, while steam is its gaseous form. Understanding substances helps us learn about the world around us, from the air we breathe to the food we eat.