The primary function of a stirring rod is to stir solutions by hand. Stirring rods have other uses in the laboratory, however, including helping to decant liquid from containers, breaking up emulsions and inducing crystallization.
Stirring rods are used to decant or pour liquids slowly. Slow pouring is essential when working with potentially hazardous chemicals that can react too quickly. Using the stir rod to decant liquid makes it easier to keep a precipitate in the bottom of the beaker, because the liquid pours more slowly, reducing the chances of it agitating the solid.
To induce crystallization in a recrystallization experiment, the glass stirring rod is scraped against the inside of the flask containing the solution.