<?php
$txt_file = "counter.txt";

if(file_exists($txt_file)) {
    $f = fopen( $txt_file, 'r+' );
    $count = fread($f, filesize($txt_file));
    rewind($f);
    $count++;
    fwrite($f, $count);
    ftruncate($f, ftell($f));
    fclose( $f );
} else {
    print "File Not Found";
}

$s = $count;
$line = sprintf("%s people have visited the site.", $s);
print $line;
?>

$txt_file = "counter.txt";

This variable is the text file.

if ( file_exists($txt_file) )
	{

If the file is found continue, or print an Error.

$f = fopen( $txt_file, 'r+' );

Open the text file so we can read out the count value.

$count = fread( $f, filesize( $txt_file ) );

Read the text file, and fill the $count variable with the result.

rewind( $f );

Move the pointer to the beginning of the file

$count++;

Increment the $count value by "1".

fwrite( $f, $count );

Write the new number to the text file.

ftruncate( $f, ftell( $f ) );

Get rid of any extra space in the file that might exist from writing to it.

fclose( $f );
}

Close the text file, since we are finished with it.

else 
	{
	print "File Not Found";
	}

If the file was not found print an error.

$s = $count;

Move the $count variable to a new variable "$s".

$line = sprintf("%s people have visited the site.", $s);

Create a string that will print to the user, displaying the new $count number.

print $line;

Last but not least, we print the line back to the user.

That is the end of the counter tutorial. Now you should have a better understanding on it.