What are some common challenges faced by PHP beginners when setting up a forum on a website?

```php
// Check if user is logged in before allowing access to forum
session_start();
if(!isset($_SESSION['user_id'])){
    header('Location: login.php');
    exit;
}
```

Another challenge is implementing a way to display and organize forum threads and replies in a structured manner. This can be achieved by using database queries to retrieve and display the necessary information in a user-friendly format.

```php
// Retrieve and display forum threads and replies
$query = "SELECT * FROM threads ORDER BY created_at DESC";
$result = mysqli_query($connection, $query);

while($row = mysqli_fetch_assoc($result)){
    echo "<h3>{$row['title']}</h3>";
    echo "<p>{$row['content']}</p>";
    // Display replies for each thread
    $query_replies = "SELECT * FROM replies WHERE thread_id = {$row['id']}";
    $result_replies = mysqli_query($connection, $query_replies);
    while($row_reply = mysqli_fetch_assoc($result_replies)){
        echo "<p>{$row_reply['content']}</p>";
    }
}
```

Lastly, beginners may struggle with implementing features such as pagination, search functionality, and user profile management within the forum. These features can be achieved by utilizing PHP frameworks or libraries to streamline development and enhance functionality.

```php
// Implement pagination for forum threads
$per_page = 10;
$page = isset($_GET['page']) ? $_GET['page'] : 1;
$start = ($page - 1) * $per_page;

$query = "SELECT * FROM threads ORDER BY created_at DESC LIMIT $start, $per_page";
$result = mysqli_query($connection, $query);

while($row = mysqli_fetch_assoc($result)){
    echo "<h3>{$row['title']}</h3>";
    echo "<p>{$row['content']}</p>";
}

// Add pagination links
$query_total = "SELECT COUNT(*) as total FROM threads";
$result_total = mysqli_query($connection, $query_total);
$row_total = mysqli_fetch_assoc($result_total);
$total_pages = ceil($row_total['total'] / $per_page);

for($i = 1; $i <= $total_pages; $i++){
    echo