Functions are created/ defined then they are called.

Defining a function:

  // Function definition
  
  function calculateBill() {
  	// this is the function body
  	console.log('running calculateBill');
  }

Calling a function:

  // Function call or run
  
  calculateBill(); // running calculateBill (returns undefined)

Variables created inside a function are not available outside the function. e.g. total above.

It is a temporary variable. After running of the function is complete, the variable is cleaned up or garbage-collected.

Returning value from function:

  function calculateBill() {
  	const total = 100 * 1.13;
  	return total; // total is returned
  }
  
  calculateBill(); // returns 112.999999999

Capturing returned value from a function into a variable:

const myTotal = calculateBill(); (myTotal will have value 112.999999999)