The Muller method is used to find the roots of polynomial equations. It estimates roots by determining the intersection of a line through two y-values of the function with the x-axis. The method improves on the secant method by fitting a parabola through three points instead of a line, allowing a more accurate estimated root to be calculated using the quadratic formula. Specifically, it generates a system of equations from three points to solve for the coefficients of the parabola, then finds where it intersects the x-axis to give a new estimated root.