A text-based game is like a storybook that you can interact with. Instead of looking at pictures and reading the words, you type in what you want your character to do or say. The computer then responds with what happens next based on your choices.
For example, imagine a game where you are a detective trying to solve a mystery. The computer might tell you that you are in a dark alley and see a suspicious figure standing in front of you. It will then ask you what you want to do. You can type in things like "approach the figure" or "turn and run away."
Based on what you choose, the computer will tell you what happens next. It might say that you approach the figure and they turn out to be a harmless bystander, or that you turn and run away and miss a clue that could have helped you solve the mystery.
So, a text-based game is like a book where you get to make choices and the story changes based on what you choose.