An LED is a semiconductor device that emits light when an electric current passes through it. LEDs are used in a variety of applications, including automotive lighting, computer and electronics displays, general lighting, and portable lighting. Many LEDs have a built-in resistor that limits the amount of current that can pass through the LED, so they can be connected directly to a power source without requiring additional circuitry.
To make an LED flash, you need to apply a constant voltage to it. The voltage must be high enough to overcome the built-in resistance of the LED so that current can flow through it. The current flowing through the LED will cause it to emit light. The intensity of the light will depend on the forward voltage of the LED and the amount of current flowing through it.
To make an LED flash at a specific rate, you need to use a circuit called an astable multivibrator. This type of circuit generates square wave pulses that can be used to drive the LED. The frequency of the pulses can be adjusted by changing the values of resistors or capacitors in the circuit.