Reactants turn into products.
#2"H"_ (2(g)) + "O"_ (2(g)) -> 2"H"_ 2"O"_ ((l))#
In this equation, hydrogen and oxygen are the reactants because they are on the left side of the chemical equation. Reactants are the parts of the equation that actually react, whereas products are what the reactants turn into. Products are the result of the reaction; in this example, the product is water.
Think of reactants like