According to Reference.com, the purpose of titration is to find the concentration of an unknown acid or base in a solution. It works by gradually combining a base of known concentration with an unknown acid solution, or vice versa, until the solution is neutralized.
The point at which neutralization occurs is called the equivalence point and is often indicated by a color change. Phenolphthalein is one commonly used equivalence point indicator. It turns colorless in acids and red in bases.
Once the equivalence point is observed, the concentration of the known substance can be used to calculate the molarity of the unknown substance.