To declare function, you start with a key word "function"

function function_name ($with_argument)

{

coding block;
//when you need to return the result to the called

return($with_argument);

}

<?php
function simple_parameter($with_argument)
{
echo " Acaller has called this function with a parameter <font color='#FF0000'>$with_argument </font><br>";
return "Hi: <font color='#FF0000'>$with_argument </font>welcome to world of php <br>";
}
//calling function
echo simple_parameter("Manas");
// calling a function with parameter to the argument
simple_parameter("baba");
//this will print at local area
echo simple_parameter("caller");
?>