Chemical equations indicate the species involved in a reaction (reagents) and those resulting from the reaction (products). Reagents, on the left, are separated by an equal sign or an arrow from the products. Reagents and products have as prefixed a number indicating in what molecular proportion the reagents are combined to form the products.
These prefixes, called stoichiometric coefficients, are usually integers but in some cases you can use fractional numbers. The equation must be adjusted so that reactants and products have the same number of atoms.