A compound is a substance that contains atoms of two or more different elements, and these atoms are chemically joined together. For example, water is a compound of hydrogen and oxygen. Each of its molecules contains two hydrogen atoms and one oxygen atom. There are very many different compounds.

Water: two hydrogen atoms and one oxygen atom joined together.Water
Carbon dioxode: two oxygen atoms and one carbon atom joined togetherCarbon dioxide

An introduction to atoms and elements found in everyday objects