Q: Additional elements to URLS? I'm not sure what the terminology is, but basically I have a site that uses the "tag-it" system, currently you can click on the tags and it takes the user to
topics.php?tags=example

My question is what sort of scripting or coding would be required to be able to add additional links?
topics.php?tags=example&tags=example2

or
topics.php?tags=example+example2

Here is the code in how my site is linked to tags.
header("Location: topics.php?tags={$t}");

or
<a href="topics.php?tags=<?php echo $fetch_name->tags; ?>"><?php echo strtolower($fetch_name->tags);?></a>

Thanks for any hints or tips.

A: You cannot really pass tags two times as a GET parameter although you can pass it as an array
topics.php?tags[]=example&tags[]=example2

Assuming this is what you want try
$string = "topics.php?";
foreach($tags as $t)
{
    $string .= "tag[]=$t&";
}
$string = substr($string, 0, -1);

We iterate through the array concatenating value to our $string. The last line removes an extra & symbol that will appear after the last iteration 
There is also another option that looks a bit more dirty but might be better depending on your needs
$string = "topics.php?tag[]=" . implode($tags, "&tag[]=");

Note Just make sure the tags array is not empty

A: 
topics.php?tags=example&tags=example2
  will break in the back end;

you have to assign the data to one variable:
topics.php?tags=example+example2
looks good you can access it in the back end explode it by the + sign:
//toplics.php
<?php
    ...
    $tags = urlencode($_GET['tags']);
    $tags_arr = explode('+', $tags); // array of all tags

    $current_tags = ""; //make this accessible in the view;
    if($tags){
         $current_tags = $tags ."+"; 
    }
   //show your data
?>

Edit:
you can create the fron-end tags:
<a href="topics.php?tags=<?php echo $current_tags ;?>horror">
    horror
</a>

