Clarify INSTALL.txt

let me understand this better when i do the coding.

" If you are running
Windows make sure you encode the file with the UNIX standard or the
code will not be detected."

$GLOBALS['simpletest_installed'] = TRUE;
if (preg_match("/^simpletest\d+$/", $_SERVER['HTTP_USER_AGENT'])) {
$db_prefix = $_SERVER['HTTP_USER_AGENT'];
}

step 2. a requirement? What am i looking for and what do i do if needed?
where i see install_main(). but what am i exactly looking for in what line where?

2. It is highly recommended, but not necessary, that you add the following
code to install.php at the beginning of install_main(). Should look like
7.x branch of Drupal core.

// The user agent header is used to pass a database prefix in the request when
// running tests. However, for security reasons, it is imperative that no
// installation be permitted using such a prefix.
if (preg_match("/^simpletest\d+$/", $_SERVER['HTTP_USER_AGENT'])) {
header('HTTP/1.1 403 Forbidden');
exit;
}
I'm in a major confusion and need better instructions on this step as I'm extremely confused.

3. If there are any test modules they will be displayed on the admin modules
page (admin/build/modules) unless the following code is added to
modules/system/system.admin.inc in system_modules() just after:
"$files = module_rebuild_cache();".

// Remove hidden modules from display list.
foreach ($files as $filename => $file) {
if (!empty($file->info['hidden'])) {
unset($files[$filename]);
}
}

What exactly do i remove and what lines are these in?
If i attach these files would someone be able to alter them for me since I'm not a programmer?

Any bit of help would be greatly appreciated.