How can i make a community forum (like this site)???

Short expert note: @webdesigner65 followed the tutorial suggested by @deceptikon, created the database and edited the connection file, and can see the index under XAMPP while "home", "make category" and "create topic" fail. Below are focused, practical checks and fixes that match the usual causes for that exact symptom.

1. Enable PHP errors first and read the logs (PHP and Apache).
2. Verify the active DB connection from each page (sometimes the index uses a different include path). Test queries in phpMyAdmin.
3. Confirm table names and any prefix used by the code match the actual tables. A single typo or prefix mismatch will show the front page but break posting actions.
4. Check session/permission logic: pages that let you create categories/topics often require an "admin" flag or a logged-in session. Make sure session_start() runs before any permission checks.
5. Look for .htaccess/mod_rewrite dependencies (friendly URLs will fail if mod_rewrite is off).
6. Check encoding and PHP tags: files must be UTF-8 without BOM and use <?php (not short tags) unless short_open_tag is enabled.
7. If running a modern PHP version, legacy mysql_* calls will fail—migrate to mysqli or PDO.

Common quick fixes: manually set an admin flag in the users table if category creation is hidden behind permissions; correct any include/require paths that differ when pages are loaded from subfolders; enable mod_rewrite in Apache if the tutorial used pretty URLs.

Quick test snippet to drop in as a one-off file (do not leave in production):

<?php
ini_set('display_errors',1);
error_reporting(E_ALL);

$mysqli = new mysqli('localhost','db_user','db_pass','db_name');
if ($mysqli->connect_error) { die('DB connect error: '.$mysqli->connect_error); }
echo "DB OK";
?>

Note: turn off display_errors on a public server and remove test files after debugging. As @Member#120589 observed, debugging takes time; methodical checks above usually find the culprit.