Problems
There are a host of problems with your code as it stands...
- Forms posted to PHPuse thenameattribute in the$_POSTsuperglobal
- Therefore you are effectively not submitting anything when you submit your form
- Add the name="..."attribute to each of your form elements to fix this
 
- Your ifstatements are by and large redundant
- Not least because you don't post anything as per point 1
 
- You should be using prepared statements for user generated input to protect your database from attack and or corruption
- Your code is generally confusing and not laid out very well
- I'm not sure what half of your brackets,ifsandfunction callsare supposed to be doing
 
- The noticeyou're getting is because you never set$searchin yourPHP
Solution
N.B
- This assumes that all of the code is in the one file [`checkorderstatus.php] and that it submits to itself.
Additional note:
I'm not sure that LIKE '%...% is the best solution here. It appears you're looking for id which, presumably (?) is a number? In which case I would simply user:
WHERE deliverystatus.statusid = SEARCH_ID
The below code follows that premise. If however you are indeed in need of LIKE then you should update the query like:
WHERE  deliverystatus.statusid LIKE ?
and update the search term in the code:
$search = "%".$_POST["search"]."%";
Updated HTML form
<form action="checkorderstatus.php" method="post">
    <input id="search" name="search" type="text" placeholder="Type here">
    <input id="submit" name="submit" type="submit" value="Search">
</form>
Using mysqli
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT); 
$mysqli = new mysqli ($hn, $un, $pw, $db);
if(isset($_POST["submit"])){
    $search = $_POST["search"];               // Prepare the search term
    $sql   = "SELECT statusdescription FROM deliverystatus WHERE deliverystatus.statusid = ?";
    $query = $mysqli->prepare($sql);          // Prepare the statement
    $query->bind_param("i", $search);         // Bind search valus as an integer (use "s" if it's a string)
    $query->execute();                        // Execute the query
    $query->store_result();                   // Store the result
    $query->bind_result($status_description); // Bind "statusdescription" to a varaible
    while($query->fetch()){                   // Loop through result set
        echo $status_description}."<br>";     // Echo each match to a newline
    }
}
Using PDO
$pdo = new pdo(
    "mysql:host={$hn};dbname={$db}", $un, $pw,
    [
        PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
        PDO::ATTR_EMULATE_PREPARES => FALSE
    ]
);
if(isset($_POST["submit"])){
    $search = $_POST["search"];                   // Prepare the search term
    $sql   = "SELECT statusdescription FROM deliverystatus WHERE deliverystatus.statusid = ?";
    $query = $pdo->prepare($sql);                 // Prepare the statement
    $query->execute([$search]);                   // Execute the query binding search as the parameter
    while($result = $query->fetchObject()){       // Loop through result set
        echo $result->statusddescription."<br>";  // Echo each match to a newline
    }
}