Okay kiddo, do you know what a candle is? It's a stick made out of wax or other material that you light up with a match or a lighter. When you light up the candle, it produces a small flame that gives off light.
Now imagine that instead of holding the candle with your hands, you put it on a special stand called a candlestick. The candlestick is designed to hold the candle in place so that it doesn't fall over.
When you put the candle on the candlestick and light it up, the flame produces light that can be seen from all around. The light shines brightly because there's nothing in the way to block it. This is why people often use candlesticks in the home during power outages or for special occasions like birthday parties or religious ceremonies.
So in short, the light upon the candlestick refers to the light that comes from a lit candle when it's placed on a special stand called a candlestick.