Each segment of the display is labeled from "a" to "g" and represents a specific part of the digit or character. When a particular segment is illuminated, it creates the appearance of that segment being lit up, while the others remain off.

To control the segments of a 7 segment LED display, each segment is connected to a microcontroller pin or a driver circuit. The common method of connection is either common cathode or common anode configuration.

In a common cathode configuration, all the cathodes of the LED segments are connected together and connected to the ground (GND), while the anodes of each segment are connected to individual microcontroller pins. When a particular segment needs to be illuminated, the corresponding microcontroller pin is set to a high logic level (typically 5V) to allow current flow through that segment, while the common cathode remains grounded.

In a common anode configuration, all the anodes of the LED segments are connected together and connected to a positive voltage source (VCC), while the cathodes of each segment are connected to individual microcontroller pins. When a particular segment needs to be illuminated, the corresponding microcontroller pin is set to a low logic level (typically 0V) to allow current flow through that segment, while the common anode remains at the positive voltage source.

By selectively controlling the state of each segment, the microcontroller can display different digits or characters on the 7 segment LED display. This is achieved by rapidly switching between the segments to create the illusion of a continuous display.

In summary, a 7 segment LED display works by selectively illuminating different segments to form numbers or characters. The segments are controlled by a microcontroller or driver circuit using either a common cathode or common anode configuration.