Should probably have explained what I did, sorry about that.
A string, such as $string in the above code, is simply an array of characters. To navigate an array, you choose the index that you want to move to. Such as the following:
$string = "asdfadfnglkaslkngalkfnk2342419!1342@sadfadsfad?123412341adfafa"
where 0 and 12 are indexes in the array.
So what I did was used the Get-Random cmdlet and limited the results to between 0 and the length of the string. Get-Random returns and int value and that is used to navigate the character array.