An object-oriented user interface is like a toybox with different toys in it. Each toy is its own object and does different things. They can be picked up, moved around, and played with.
In the same way, an object-oriented user interface is a way for people to interact with a computer program. Each part of the program is like a toy, and can be moved around and interacted with by the user.
For example, imagine a program that helps you design a house. One toy might be a window, another a door, and another a wall. You can click on each toy and move it around, resize it, and change its color.
The cool thing about an object-oriented user interface is that it makes it easy for programmers to create new toys and put them in the toybox. They can create tools that do new things, like a tool that lets you draw a floor plan or a tool that lets you put furniture in a room.
Overall, an object-oriented user interface is like a fun, interactive way to use a computer program. It's like a toybox full of different toys that you can play with and use to create something new.