Predefined/Built-in Function:
The phrase "I love to count!" contains 16 characters. User Defined Function: 5 + 10 = 15
7 + 13 = 20
2 + 4 = 6

Explanation: Functions allow the user to program complex tasks more easily. The example of the predefined/built-in function counts the characters in the phrase. The example of the user defined function returns the answer to the sum of the two numbers.