Chemical formulas can be used to describe the relative amounts of elements present in a compound.
For example, the chemical formula for water is H2O: this means that each molecule of water is constituted by 2 atoms of hydrogen (H) and 1 atom of oxygen (O).
In this way, compounds will have unique names which can describe their elemental composition.
[1] The chemical composition of a mixture can be defined as the distribution of the individual substances that constitute the mixture, called "components".
In other words, it is equivalent to quantifying the concentration of each component.