Linux, Apache, MySQL, PHP

$output=fopen("testfile.txt","r") or exit("Unable to open file!"); <--- $output is a file resource, this is not the file content.

//(2) Then we can get rid of the"," in there:
$output = str_replace(","," ", $output); <--- he takes the $output which is a file resource and does a string replace on it and re-assigns the variable $output as a string.
//(3) Then we explode it at every ,encountered
//$output = explode(",",$output); <--- when this is uncommented it will change a string into an array. If the source string has no "commas" in it it will return an array with one value. you could also say if(count($output)==1)) {echo "I have 1!";}else{echo "I'm Lost!";}, but currently it does nothing as it is commented out so $output should still be a string.
echo "output"; <--- echos a string called "output"
echo $output; <--- echoes a variable currently a string and most likely just the name of the file resource returned from the fopen call.
foreach($output as $var) <--- in a foreach the first argument MUST be an array!, it is a string right now and so reports an error.
{
	echo " ";
	echo"display each value as array ";
	echo $var;
}