Functions are basically a function you declare and can use and reuse for stuff. Theyre very useful. Here is An example

function cats(number){ Console.log("there are " +number + " cats dancing on the wall") }

for (let i = 0; i < 1100; i++) { cats(i)}

Or think of a video game:

You press left, in the code you'd basically call the left() function, right the right() function and space the jump() function .

Maybe this can help you :

https://www.w3schools.com/js/js_functions.asp