PHP - Insecure Php

Hello,
          I'm trying to create a Content Management System (CMS) however, I always feel that my code is insecure and unprofessional. For example, here is some context from my core file:
         
          Code: [Select]
public function getSiteData() {
  $q = "SELECT * FROM siteSettings ORDER BY id DESC LIMIT 1";
  $r = mysql_query($q);
 
  while ( $a = mysql_fetch_assoc($r) ) {
  global $siteName, $siteMotto, $siteIco;
  $siteName = $a['site_name'];
  $siteMotto = $a['site_motto'];
  $siteIco = $a['site_ico'];
        }
  }

 public function adminGet() {
    $q = "SELECT * FROM testDB ORDER BY created DESC LIMIT 4";
    $r = mysql_query($q);

    if ( $r !== false && mysql_num_rows($r) > 0 ) {
      while ( $a = mysql_fetch_assoc($r) ) {
        $title = stripslashes($a['title']);
        $bodytext = stripslashes(substr($a['bodytext'],0,100));
I seem to feel that the solutions that I approach towards my content management system are insecure, and could lead to easy hacks and injections. Now, when I compare my code to other content management systems, I seem to  see a huge difference in there professional layout, and the way they go about their coding.  I'm only 14, and have been studying PHP for around a year and a half now, I'm wanting to become a little more advanced in PHP, but I can't feel like I can due to my insecure coding. Would anybody be able to point me in the right direction, or tell me where I'm going wrong please?

I have MSN and Yahoo, if you'd prefer to contact me that way. MSN: jarrod@tichiegaming.com : Yahoo: Ptsface12.

Many thanks,
Jarrod