A resource in Windows is something that a program can use to make its job easier. It's kind of like a helper that the program can call on when it needs something.
For example, let's say you were building a house out of LEGOs. You might use a LEGO piece that's shaped like a window to help you build the walls. That LEGO piece is like a resource – it's something that helps you get the job done more easily.
In Windows, resources can be all kinds of things – pictures, icons, sounds, fonts, and more. Programmers can include these resources in their programs so that they don't have to create them from scratch every time. That way, the program is faster and more efficient.
So think of resources like tools in a toolbox – they're there to help a program do its job better and more easily.