Okay kiddo, so let's say you have some toys and your friend has some toys too. You want to trade your toys with your friend so you can both have more toys to play with.
Now imagine the same thing is happening with countries. They want to trade things they make or grow with other countries so they both have more things to use and sell.
The trade-to-gdp ratio is a way to figure out how much trading a country is doing compared to how big their economy is. It's like figuring out how many toys you traded with your friend compared to how many toys you have in total.
If a country has a high trade-to-gdp ratio, that means they are doing a lot of trading compared to how big their economy is. If a country has a low trade-to-gdp ratio, that means they don't do as much trading compared to their economy.
It can be important to know these ratios because if a country does a lot of trading, that can help their economy grow. But if they rely too much on trading with other countries and something goes wrong, it can hurt their economy too. Just like if you traded too many of your favorite toys with your friend and then they moved away and you couldn't play with them anymore.