Do kotlin functions have to be in the main function code example

Example 1: function kotlin

// Declare a function in Kotlin
fun happyBirthday(name: String, age: Int): String {
    return "Happy ${age}th birthday, $name!"
}
// Call function
val greeting = happyBirthday("Anne", 32)

Example 2: how to write a function in kotlin

// Use 'fun' keyword to declare function
// 'num' is the parameter and is of type Int
// The ':Int' indicates the return type
fun square(num: Int):Int {
    return num * num
}