Вы получите обратно ассоциативный массив для каждой строки. Ключами будут имена столбцов.
include 'connect_db.php';
$stmt = $conn->query("SELECT * FROM people");
$results = $stmt->fetchAll(PDO::FETCH_ASSOC);
foreach ($results as $row) {
echo $row['some_column_name'] . '<br>';
}
или
include 'connect_db.php';
$stmt = $conn->query("SELECT * FROM people");
$results = $stmt->fetchAll(PDO::FETCH_ASSOC);
foreach ($results as $row) {
foreach ($row as $key => $value){
echo $key . ', ' . $value . '<br>';
}
}