Nixie tubes are like magic boxes that light up with numbers or letters inside. These tubes are made of glass and contain a special gas that lights up when electricity passes through it.
When we want to display a number, the electricity flows through the tube and lights up the appropriate number. For example, if we want to show the number 5, the electricity lights up the little "5" shape inside the tube, so we can see it glowing.
The cool thing about nixie tubes is that they were mostly used a really long time ago in clocks and other types of electronics. Nowadays, they have become popular among hobbyists who like vintage technology and want to use them to make retro-looking displays or intriguing art installations.