PHP连接到Web服务器

I am typically new to using an online web server. 000webhost.com is a free web hosting server site that provides a database and you can also connect your website with it. I have created my database fine and when I have tried to connect the database and the website. I think the problem is within connecting to the database and I don't have any idea what do I input. this error prompts

this is how i set up my connection.

<?php
   // define database related variables
   $database = '..';
   $host = '..';
   $user = '..';
   $pass = '..';

   // try to conncet to database
   $dbh = new PDO("mysql:dbname={$database};host={$host};port={3306}", $user, $pass);

   if(!$dbh){

      echo "unable to connect to database";
   }

?>

and this is my authenticate.php

<?php 
    require 'database-config.php';

    session_start();

    $username = "";
    $password = "";

    if(isset($_POST['username'])){
        $username = $_POST['username'];
    }
    if (isset($_POST['password'])) {
        $password = $_POST['password'];

    }

    echo $username ." : ".$password;

    $q = 'SELECT * FROM users WHERE username=:username AND password=:password';

    $query = $dbh->prepare($q);

    $query->execute(array(':username' => $username, ':password' => $password));


    if($query->rowCount() == 0){
        header('Location: index.php?err=1');
    }else{

        $row = $query->fetch(PDO::FETCH_ASSOC);

        session_regenerate_id();
        $_SESSION['sess_user_id'] = $row['id'];
        $_SESSION['sess_username'] = $row['username'];
        $_SESSION['sess_userrole'] = $row['role'];

        echo $_SESSION['sess_userrole'];
        session_write_close();

        if( $_SESSION['sess_userrole'] == "admin"){
            header('Location: adminhome.php');
        }else{
            header('Location: userhome.php');
        }


    }


?>

because these are what the site has given me

I hope i can solve this right away because I will be planning to connect it thru mobile soon. Thanks in advance sirs.

Your problem is that you send data before sending a header. In your case the username:password is causing the errors. You have to echo them after all the headers and session_*. Just call the echo at the end of this script and you should be fine. And please never post any credentials (especially no DB credentials)

<?php 
require 'database-config.php';

session_start();

$username = "";
$password = "";

if(isset($_POST['username'])){
    $username = $_POST['username'];
}
if (isset($_POST['password'])) {
    $password = $_POST['password'];

}

echo $username ." : ".$password; //<-- Causing the problem

$q = 'SELECT * FROM users WHERE username=:username AND password=:password';

$query = $dbh->prepare($q);

$query->execute(array(':username' => $username, ':password' => $password));


if($query->rowCount() == 0){
    header('Location: index.php?err=1');
}else{

    $row = $query->fetch(PDO::FETCH_ASSOC);

    session_regenerate_id();
    $_SESSION['sess_user_id'] = $row['id'];
    $_SESSION['sess_username'] = $row['username'];
    $_SESSION['sess_userrole'] = $row['role'];

    echo $_SESSION['sess_userrole']; //<-- Causing the second problem
    session_write_close();

    if( $_SESSION['sess_userrole'] == "admin"){
        header('Location: adminhome.php');
    }else{
        header('Location: userhome.php');
    }


}


?>