Please explain this PHP code/syntax related to building forum pages
<p>OK so i am trying to build a forum from scratch and i realize the pages corresponding to topics will have to be generated dynamically somehow. I'm looking at a forum i frequently visit and I would like someone to explain the PHP syntax/code for the flow that I see as I have never seen the "something.php?x=something" type of structure before.</p>

<p>OK so user first visits site and the page says</p>

<pre><code>http://forumname.com/index.php?sid=someLongSetOfChars
</code></pre>

<p>(im guessing this is a session id?...what is the "?" where can i learn about it)</p>

<p>clicking login takes you to</p>

<pre><code>forumname.com/ucp.php?mode=login (what is mode? how do i know to do this?)
</code></pre>

<p>after logging in successfully you get</p>

<pre><code>forumname.com/index.php?sid=otherLongSetofChars
</code></pre>

<p>this page has the various forums in different categories.</p>

<p>Clicking on one of the categories gives:</p>

<pre><code>http://forumname.com/viewforum.php?f=1
</code></pre>

<p>Clicking on one of the topics gives:</p>

<pre><code>http://forumname.com/viewtopic.php?f=1&amp;t=192053
</code></pre>

<p>All these things sort of make sense to me (semantically) but I am wondering how they actually work and how to implement them. What variables would I have to define and where and are these pages created and stored on my server?</p>

<p>Thanks</p>
