How to send e-mail messages using PHP?

<?php
    mail("recipient@example.com",
        "This is the message subject",
        "This is the message body",
        "From: sender@example.com" . "\r\n" . "Content-Type: text/plain; charset=utf-8",
        "-fsender@example.com");
?>

How to change the default directory index page using an .htaccess file?

You can use the DirectoryIndex directive in an .htaccess file 
to specify a custom file or files that the web server looks for 
when a visitor requests a directory. To enable the DirectoryIndex 
directive, use a text editor to modify the .htaccess file as 
follows. Replace filename with the file that you want to 
display whenever a user requests the directory:

DirectoryIndex filename

You can also specify multiple filenames, and the web server
 will search for each file until it finds a match. Consider 
this example directive:

DirectoryIndex index.php index.html index.htm

How to enable and disable directory index listings using an .htaccess file?

Enable directory index listings
In some cases, however, you may want to enable index listings for a directory. 
To do this, use a text editor to add the following line to the .htaccess file:

Options +Indexes

This directive enables standard indexing, where the index listing shows 
only the filenames. You can also enable “fancy” indexing, where the 
index listing shows filenames, their filesizes, and when they were 
last modified. To do this, add the following line to the .htaccess file:

IndexOptions +FancyIndexing

How to protect your file content using htaccess?

# Prevent Apache from serving .htaccess files:
<FilesMatch "^\.htaccess">
    Order allow,deny
    Deny from all
</FilesMatch>

How to enable and disable the PHP magic quotes directive?

When the magic quotes directive is enabled, PHP automatically escapes 
data from HTTP GET and POST requests and cookie data. For example, 
if a user types “hello” (with the quotation marks) in a form, PHP 
automatically escapes the quotation marks and stores the value as 
\“hello\”. To enable this functionality, use a text editor to 
modify the magic quotes directive in the php.ini file as follows:

magic_quotes_gpc = on

To disable this functionality, modify the magic quotes directive in the php.ini file as follows:

magic_quotes_gpc = off

How to enable and disable the PHP register_globals directive?

When the register_globals directive is enabled, PHP creates variables 
automatically from HTML form parameters and cookie data. 
To enable this functionality, use a text editor to modify the 
register_globals directive in the php.ini file as follows:

register_globals = on

To disable this functionality, modify the register_globals 
directive in the php.ini file as follows:

register_globals = off

How to enable and disable the PHP allow_url_fopen directive?

To enable this functionality, use a text editor to modify 
the allow_url_fopen directive in the php.ini file as follows:

allow_url_fopen = on

To disable this functionality, modify the allow_url_fopen 
directive in the php.ini file as follows:

allow_url_fopen = off