Add data from front end into custom made table in database

Question

I have a registration form which contains firstname, lastname, organisation, username, email etc. Here Username and email only will be saved in the db in the wp_users table.
I have created a new table called wp_userdata to show all other details such as firstname, lastname, organisation etc.

Now I need to know how I can make the data from front end to be added in the custom table I have created. The following code is the one which I use to create the registration form. Someone please help me.

<div id="tab2_login" class="tab_content_login" style="display:none;">
        <h3>Sign Up</h3>
        <p>We encourage you to do a one-time signup with us to be able to download content from this website</p>
        <form method="post" action="<?php echo site_url('wp-login.php?action=register', 'login_post') ?>" class="wp-user-form">
            <div class="username">
                <label for="title"><?php _e('Title'); ?>: </label>
                <Select>
                    <option>Mr</option>
                    <option>Ms</option>
                    <option>Mrs</option>
                </select>
            </div>
            <div class="username">
                <label for="user_login"><?php _e('First Name'); ?>: </label>
                <input type="text" name="first_name" value="<?php echo esc_attr(stripslashes($first_name)); ?>" size="20" id="first_name" tabindex="101" required/>
            </div>
            <div class="username">
                <label for="user_login"><?php _e('Middle Name'); ?>: </label>
                <input type="text" name="middle_name" value="<?php echo esc_attr(stripslashes($middle_name)); ?>" size="20" id="middle_name" tabindex="101" />
            </div>
            <div class="username">
                <label for="user_login"><?php _e('Last Name'); ?>: </label>
                <input type="text" name="last_name" value="<?php echo esc_attr(stripslashes($last_name)); ?>" size="20" id="last_name" tabindex="101" required/>
            </div>
            <div class="username">
                <label for="user_login"><?php _e('Username'); ?>: </label>
                <input type="text" name="user_login" value="<?php echo esc_attr(stripslashes($user_name)); ?>" size="20" id="user_login" tabindex="101" required />
            </div>
            <div class="password">

                <label for="user_email"><?php _e('Email Address'); ?>: </label>
                <input type="text" name="user_email" value="<?php echo esc_attr(stripslashes($user_email)); ?>" size="25" id="user_email" tabindex="102" required/>
            </div>
            <div class="password">
                <label for="organisation"><?php _e('Organisation'); ?>: </label>
                <input type="text" name="organisation" value="<?php echo esc_attr(stripslashes($user_org)); ?>" size="25" id="organisation" tabindex="102" />
            </div>
            <div class="password">
                <label for="Designation"><?php _e('Designation'); ?>: </label>
                <input type="text" name="Designation" value="<?php echo esc_attr(stripslashes($user_desig)); ?>" size="25" id="designation" tabindex="102"/>
            </div>

            <div style="width:100px;position:relative;float:left;margin: 7px 0 0 0;">
                <input type="button" name="user-cancel" value="<?php _e('Cancel'); ?>" id="user-cancel" tabindex="103" />
            </div>
            <div class="login_fields">
                <?php do_action('register_form'); ?>
                <input type="submit" name="user-submit" value="<?php _e('Sign up!'); ?>" class="user-signup" tabindex="103" />
                <?php $register = $_GET['register']; if($register == true) { echo '<p>Check your email for the password!</p>'; } ?>
                <input type="hidden" name="redirect_to" value="<?php echo $_SERVER['REQUEST_URI']; ?>?register=true" />
                <input type="hidden" name="user-cookie" value="1" />
            </div>
        </form>
    </div>