User modeling is a way for computers to understand what people like or don't like, so they can show them content that they will enjoy. Just like how your mommy or daddy knows what you like to eat, and what toys you like to play with, computers can also learn what you like.
For example, when you watch videos on YouTube, YouTube learns what types of videos you like to watch, and suggests similar videos for you. This is because YouTube is creating a model of who you are as a user, based on things like what you watch, how long you watch for, and more.
This is important because it helps websites and apps give us personalized experiences that are tailored to our preferences. And that makes it easier for us to find what we want and enjoy using them more.
So user modeling is like a smart friend, who knows what we like and gives us things that we will love.