Chemical formulas can have three components. The Elemnts__ which are represented by a single uppercase letter, or represented by an uppercase letter followed by a lowercase letter. This tells you the types of elements in the compound.
The which are numbers that are found on the lower - hand side of each element symbol. This tells you the number of of this element in the molecule. If an element symbol has no subscript next to it, then this indicates that there is only atom of this element in the molecule.
The which surround some groups of atoms indicate that the numbers of all of the atoms inside the bracket need to be by the on the outside of the bracket found on the lower - hand side of that bracket.