<input type="text" name="names" placeholder="Enter Name" />
<select name="gender">
    <option value="Male">Male</option>
    <option value="Female">Female</option>
</select>
<input type="text" name="age" placeholder="Enter Age" />
<input type="text" name="state" placeholder="Enter State" />

<label>How Did You Find Us?</label>

<input type="checkbox" name="remarks[]" value="Search Engine (eg. Google)"> Search Engine (eg. Google) &nbsp;&nbsp;&nbsp;
<input type="checkbox" name="remarks[]" value="Facebook"> Facebook &nbsp;&nbsp;&nbsp;
<input type="checkbox" name="remarks[]" value="Newspaper Ads"> Newspaper Ads &nbsp;&nbsp;&nbsp;
<input type="checkbox" name="remarks[]" value="Bus-Stop Ads"> Bus-Stop Ads &nbsp;&nbsp;&nbsp;

$names = filter_input(INPUT_POST, "names");
$gender = filter_input(INPUT_POST, "gender");
$age = filter_input(INPUT_POST, "age");
$state = filter_input(INPUT_POST, "state");
$remarks = $_POST['remarks'];

$inputArr[] = array(
    $names, $gender, $age, $state, $remarks
);

$fp = fopen($_SERVER["DOCUMENT_ROOT"]."/student.csv", "a+");

fputcsv($fp, $inputArr);
fclose($fp);

Array
(
    [0] => Melinda
    [1] => Female
    [2] => 23
    [3] => united state
    [4] => Array
        (
            [0] => Facebook
            [1] => Newspaper Ads
            [2] => Bus-Stop Ads
        )

)

Array
(
    [0] => Melinda
    [1] => Female
    [2] => 23
    [3] => united state
    [4] => Array
    [5] => Facebook
    [6] => Newspaper Ads
    [7] => Bus-Stop Ads
)