A function generator is a device that produces various waveforms such as square, triangular, and sinusoidal signals. It operates through frequency control networks involving capacitors for charging and discharging currents. The upper constant current supplies steady input to the integrator over time while the lower component causes linear decreases in output voltage with time. A multivibrator changes state at a predetermined maximum level of integrator output voltage, shaping the waveform's amplitude dynamically.