Quadratic functions are modeled by the equation y = ax^2 + bx + c, where a ≠ 0. They produce U-shaped parabolic graphs. Many real-world phenomena follow quadratic patterns, like water in a fountain or a basketball's trajectory. The lowest or highest point on a parabola is the vertex. To graph a quadratic function in standard form, you first find the vertex by calculating -b/2a, then plot the axis of symmetry and other points to sketch the parabolic curve.