I believe what blk was saying is that he was doing something like $_GET[$mycharset[$a].$mycharset[$b]].
However that code is used on a PHP server and not on a client, when you're a client you need to send a HTTP request, in this case you'll request the page site.com/asdsdasd.html since you're bruteforcing the URL, it means you're using the GET method and not the POST, therefore a HTTP request would be like:
GET site.com/asdsdasd.html\r\n
When you're working on a PHP server and handling a website you can use $_GET["id"] to detect the value the client sent to you on that variable using the GET method.
For instance, on a forum, you can access the forum.php?section=31 which would display Hacking and Security
In PHP the code would be something like:
if("$_GET["section"]){
showsection($_GET["section"]);
}
The show section doesn't exist, I just used it so you can understand the theory.
Anyways, what matters to you is to work as a client, which means to make HTTP requests, and not to handle PHP requests.