Do you use letters instead of math? If you replace an uncertain number with a letter, it is called a variable. Simply put, the operational relationship from one variable to another is a function. For example, one variable X can get another variable Y through a calculation process, and this calculation process is a function. Of course, there are many complex properties of functions. You will learn them slowly in the future, so I won't talk about them here.

College mathematics is very complicated, so learn your current lessons well first!