En 16034 is a big set of rules that helps people make sure that a door or window they are buying is safe and will do what it's supposed to do. Imagine that you want to buy a toy, but you want to make sure it's not going to break or hurt you. You would want to read the instructions on the box, check if it has any warning labels, and look for any certifications that show that it has been tested and found to be safe. In the same way, en 16034 is like an instruction manual and certification for doors and windows.
The en 16034 rules help people who make doors and windows to follow certain standards when they design and build them. They have to make sure that the doors and windows are strong enough to keep you safe, that they won't easily catch fire, that they are energy efficient, and that they can be opened and closed easily. They also need to make sure that they have tested the doors and windows to make sure they do what they are supposed to do, and they need to put labels on them to show what kind of protection they offer.
So, when you buy a door or window that meets en 16034 standards, you can be sure that it has been designed and tested to keep you safe and comfortable in your home. It's like having a grown-up who knows how to pick out the best toys for you, but instead, they are making sure you have the best doors and windows for your house!