How Make PHP as Plugin?

[Nuss]

i need to trasnform a PHP to Vb plugin

For example if i have

PHP Code:

<?
if(some condition){
echo 'hello world';
}else{
echo 'Good bye';
}
?>

(This is only example, my php is much more complicated)

So i need to trasform it to Plugin and call it in some Template with $my_php_plugin

How can do it??

Tanks in advance ppl!!