To insert all data from the form in the database, you'll have to modify this part of the code:
$Title = mysqli_real_escape_string($link, $_POST['Title']);
$sql = 'INSERT INTO library SET
Title="' . $title . '",
$error = 'Error adding submitted item: ' . mysqli_error($link);
You will want to validate the inserted values (for example: all fields need to have a value), and sanitize them using mysqli_real_escape_string (like you already do with the title). And then you add them to the INSERT query.
To display all the values, you have to modify this part of the code:
$result = mysqli_query($link, 'SELECT Title FROM library');
$error = 'Error fetching library items: ' . mysqli_error($link);
while ($row = mysqli_fetch_array($result))
$title = $row['Title'];
Add all column you want to get from the library table in the SELECT query. Then, in the while loop, put those values in arrays like you already do with the title.
In items.html.php, you'll have to use those arrays to actually display the values (like you already do with the title).