When you want to use a computer program, you need a file that tells the computer what to do. That file is called an executable. It's like a recipe that the computer follows to make the program work, just like how you follow a recipe to bake a cake.
Sometimes, people make changes to the program so it works better. When they do, they make a new executable file that has the changes in it. It's like they made a new recipe with better instructions for baking the cake.
When you download and install the new executable on your computer, it will use the updated recipe to run the program better than before. So you get a better experience with the program because the new executable has improved it.
That's what a new executable is: it's a new recipe that makes the program work better.