Twitter Bootstrap CMS Ok, so I started to build my own CMS. You can see Aleksandar Golubovic's Blog,and I need your help. Please, look at my code, and tell me is that safe? You can download current version from Twitter Bootstrap CMS. If you want to install it, just read instructions.

So, please, tell me if I get some errors, or some of your opinions, instructions... I really need help.

EDIT:

I have many functions like:

function DeletePost()
{
if (isset($_GET['action']))
{
    if ($_GET['action']==='delete-post' &amp;&amp; !isset($_GET['id']))
    {
        $qry=mysql_query("SELECT * FROM posts ORDER BY id DESC");
        while ($arr=mysql_fetch_array($qry))
        {
        echo '&lt;div class="span8 offset1"&gt;&lt;p&gt;&lt;h3&gt;'.$arr['post_title'].'&lt;/h3&gt; &lt;a href="javascript:;" title="Delete This Post" class="delete" id="'.$arr['id'].'"&gt;Delete this post&lt;/a&gt;&lt;/p&gt;&lt;p&gt;'.$arr['post_content'].'&lt;/p&gt;&lt;/div&gt;';
        }
    }
    if ($_GET['action']==='delete-post' &amp;&amp; isset($_GET['id']))
    {

            $del=$_GET['id'];
            $qry=mysql_query("DELETE FROM posts WHERE id='$del'") or die ("ERROR!!!");
            echo "This post has been successfull deleted.";


    }
}
}


And this function is included in some page. So my question is: Is this method safe?
Note: All functions is separeted pages using .htaccess
Well looking at this as a code review of the code you posted i can recommend a couple of things;

Security

The major flaw at the moment is the possibility for SQL injection. You put the $_GET values directly into the query without validation or escaping. 

PHP.net has a page on SQL injection:  http://php.net/manual/en/security.database.sql-injection.php

Deprecated code

It is strongly recommend not to use the mysq_* functions. !!!

These functions are deprecated and will recieve no more support and will be removed in an upcoming version of PHP. See http://php.net/manual/en/function.mysql-connect.php and look at the big red box. This is potentially a huge security hazzard in the future as well.

User Content / Access levels

Currently you are not demonstrating any check on access level. If i am to guess your actions i could delete the entire content of your website without logging in!

Database connection

You seem to open the sql connection somewhere else. Please verify for yourself that you also close the connection when request ends, avoiding lingering MySQL connections.

Misc

Also, look into the SOLID principles and PSR-2 codestyle, your current code does not match it. These are best practices and provide a good base strategy for your coding. Also, making it more likely the open source community would accept/adopt your code.

Good luck in further development of your CMS!