Photonics is the area of science and engineering where we work with light and figure out all the different things we can do with it. In my job I work on the design of lasers, so I need to understand how different materials give off light when we heat or put electricity through them. Other people then work on how we can detect light and get energy from it. This would be like designing really efficient solar cells to heat your house.
One of the biggest applications of photonics research is in high speed internet connections. Instead of sending information on the internet using electrical signals, people are now starting to use light beams and optical fibre. The speed of light is incredibly fast (670,616,629 miles per hour!!) so you can send information all around the world almost instantly. I hope that helps answer your question. Let me know if you’d like me to explain anything!