Alright kiddo, so imagine you have a bunch of toys and you want to play with them. But first, you have to figure out how to open the toy box and how to take out the toys you want to play with. That's kind of what a user interface is like.
A user interface is just a fancy way of saying the way you interact with something on a computer. It's like the toy box for your computer programs! And just like with your toys, you need to know how to get started using your programs.
Some user interfaces are easy and some are more complicated, just like some toy boxes have simple latches and others have hidden buttons. A good user interface will make it easy for you to find what you need and do what you want to do.
If you're using a phone or a tablet, you'll be tapping and swiping on the screen to get around. If you're on a computer, you might be using a mouse to click on things or typing on a keyboard to tell your program what to do.
So think of a user interface like the instructions for using a new toy - it might seem complicated at first, but once you learn how to use it, it's a lot of fun!