Functions can receive one or more parameters as arguments:

fun hello(message : String) : Unit {
     println("Hello from $message")
 }
 
 fun main(args: Array<String>) {
     hello("Kotlin")
 } 

The hello function takes a string variable as a parameter. When the hello function is called from main, a string value is passed to that function.

If the function takes more than one parameter, all parameters are separated with a comma (,). Here is another example of writing a function that takes two parameters:

fun add(a : Int, b : Int) {
     println("Result of $a + $b is ${a+b}")
}

fun main (args: Array<String>){
    add(4,5)
}

In a function declaration, variables cannot be declared with the val or var keywords, and the data type must be specified explicitly.