Alright kiddo, have you ever heard of something called a "carbon footprint"? It's basically how much pollution and greenhouse gases someone or something produces. Big companies and countries can participate in something called a "carbon trading system" where they get permits to produce a certain amount of pollution.
The EU (that's short for European Union) created their own carbon trading system called EUTL, which stands for European Union Transaction Log. It's like a big electronic book that keeps track of who has how many permits to produce pollution.
So, let's say a company wants to produce a lot of pollution. They can buy extra permits from other companies who don't need them. And if a company doesn't use up all their permits, they can sell them to other companies who need more.
This way, the EU can control how much pollution is being produced overall. The goal is to reduce the amount of greenhouse gases that are causing climate change. So even though companies are still producing some pollution, it's less than before because they have to follow the rules in EUTL.