The concept of a function is similar to something in reality.

The time of day and your position are a function. Enter 12 pm, go back to the dormitory, enter 7 am, you are in the classroom, 12 pm, you are in the canteen. You can always ask questions. Time is an independent variable and your position is a function. The set of all the positions you can get in a day is called the interval.

I should have heard a joke. Put a pig into a machine and it will come out with ham. Machine is a function, pig is an independent variable, and ham sausage is a function value. You put a cow in, export beef sausage, put a donkey in, and export donkey sausage. Put a stone in it and the machine will die. Sorry, stones don't belong to this field.

Later, you thought the ham sausage was not delicious, so you pressed the button and put it in the ham sausage. And a pig came out. This is the legendary inverse function.