#A familiar function
function Add($number1, $number2)
{
    $result = $number1 + $number2
    return $result
}

#Call the function Add. Notice we're not using Add(1,2) or Add 1, 2
Add 1 2

#We don't even need return since the last value is automatically returned
function Subtract($number1, $number2)
{
    $number1 - $number2
}

#Call it
Subtract 10 4

#Optional parameters and initialization
function Multiply([int]$number1, [int]$number2=10)
{
    $number1 * $number2
}

#Call it with just one value
Multiply 5 #returns 50

#Call it with two strings
Multiply "test" "strings" #Error: Cannot convert value "test" to type "System.Int32"

#Just for fun let's put a couple together. The parenthesis are required.
Multiply (Add 2 3) (Subtract 10 5) #returns 25