This page explanation:
Register customer information.

This page function:
Register

① Controller

Controller:/app/controller/customerController.php

class customer{
    public function action_form() {
        // ~~~
        //include view
        include_once(dirname(__FILE__) . "/../view/customer_register_form.php");
    }
}

② View

View:/app/view/customer_register_form.php

<!--~~~-->
<form action="<?= SYSTEM_DIR ?>customer/register" method="post">
    <div class="d-flex">
        //↓Label. example:last_name
        <div>顧客(性):</div>
        //↓This "input" is where you enter text.
        <input type="text" name="last_name" required>
    </div>
    <div class="d-flex">
        <div>顧客(名):</div>
        <input type="text" name="first_name" required>
    </div>
    <div class="d-flex">
        <div>ふりがな:</div>
        <input type="text" name="furigana" required>
    </div>
    <div class="d-flex">
        <div>生年月日:</div>
        <input type="date" name="birthday" required>
    </div>
    <div class="d-flex">
        <div>性別:</div>
        <select name="gender" required>
            <option value="">-</option>
            <option value="0">男</option>
            <option value="1">女</option>
            <option value="2">その他</option>
        </select>
    </div>
    <div class="d-flex">
        <div>血液型:</div>
        <select name="blood" required>
            <option value="">-</option>
            <option value="0">A</option>
            <option value="1">B</option>
            <option value="2">O</option>
            <option value="3">AB</option>
        </select>
    </div>
    <div class="d-flex">
        <div>備考:</div>
        <textarea name="note" cols="30" rows="2"></textarea>
    </div>
    <div>
        //↓This button is for submit data
        <button type="sumit" class="btn btn-primary">登録する</button>
    </div>
</form>
<!--~~~-->