You have to call the function!
Add:
write($this, $that);
to the page somewhere!
You could also change the function to:
function write($var1, $var2) {
print "I want $var1 and $var2, ok?";
}
and then run it with:
write($this, $that);
Showing that the variables inside the function don't have to match. You also don't need to put $this and $that outside the speech marks. Speech marks automactically convert variables.