Yuku free message boards

Thanks. I'm a member of two different wed development forums, and I can't get anyone on them to answer me (they never seem to understand what I'm asking).

Using a message board script as an example: In order to show the different threads, there would be a page named something like showthread.php. The thread it displayed would depend on what thread ID was pulled from the database and passed to the URL of showthread.php (for example, the URL might be something like showthread.php?id=4815162342). Showthread.php would receive the thread information using the $_GET super global array.

Here's what I can't get people to answer me on: How do you use $_GET in showthread.php to get a thread? Everyone always gives me an example such as $var = something;, then in showthread.php, it would be $_GET['var']. However, as I have explained many times to them, that's too literal; there are going to be lots of different threads on a message board. Showthread.php doesn't know if the user is going to select the thread that's information is contained in $var, or if they're going to select the thread that's information is contained in $someOtherVar. Somehow, showthread.php knows what to do no matter what thread information is passed to it, and that's what people won't explain to me.

PLEASE tell me you understand what I'm getting at.