在jquery和attr + ajax中返回false是什么

First let me show you the code

This is the script

        var user_id = $(this).attr("id");
        var datastring = 'user_two='+ user_id;
        $(".follow").click(function(){
            $.ajax({
                type: "POST",
                url: "include.php",
                data: datastring,
                success: function(html){}
            });
            $("#follow"+user_id).hide();
            $("#unfollow"+user_id).show();
            return false;
        });

Here is php

<?php 
    $query = $handler->query("SELECT * FROM users");
    while ($row = $query->fetch()) {
        $user_two = $row['id'];
        $user_one = 1;
        ?>
        <p><?php echo $row['username'];?></p>

        <?php 
            $follow_check = $handler->query("SELECT * FROM follow WHERE user_one='$user_one' AND user_two='$user_two'");
            if ($follow_check->rowCount() == 0) {?>
                <div id="follow<?php echo $user_one;?>">
                    <a href="" class="follow" id="<?php echo $user_two;?>">Follow</a>
                </div>
                <div id="unfollow<?php echo $user_one;?>" style='display:none'>
                    <a href="" class="unfollow" id="<?php echo $user_two;?>">Following</a>
                </div>
            <?php }else{?>
                    <div id="follow<?php echo $user_one;?>" style='display:none'>
                    <a href="" class="follow" id="<?php echo $user_two;?>">Follow</a>
                </div>
                <div id="unfollow<?php echo $user_one;?>" >
                    <a href="" class="unfollow" id="<?php echo $user_two;?>">Following</a>
                </div>

            <?php } ?>

 <?php } ?>

Here is the php for Insert query

<?php
include('db.php');
$user_two = $_POST['user_two'];
$query = $handler->query("INSERT INTO follow (user_one,user_two) VALUES ('1','$user_two')");

?> 

there two things i need to insert which is user_one = Session=0 or the current logged in user but i just made it static for the mean time and the user_two which is the users id or the one you will click to follow that person. But idk how to do it in ajax, like in php you can get the value of the link like <a href="?id="> and then to get the value, $_GET['id'] but idk how to store that value to script

I just need an explanation on user_id = $(this).attr("id"); and the return false inside the $(".follow").click and when I make it to false i need to refresh the page just to see the changes of links to follow and following why is it like that? By the way, When i click the follow link it will successfuly insert to the database but the user_two's value is always 0 because I dont know how to store link id to the script.

Not 100% sure if i understood but let me try:

First: id="<?php echo $user_id; ?>" it's ok. You can get it with var user_id = $(this).attr("id"); Maybe you should move this line inside the $(".follow")... block

$(".follow").click(function() {
    var user_id = $(this).attr("id"); //"this" will refer the element with the "follow" class. Then user_id will be the value of the id for the clicked element.
    $.ajax({
      type: "POST",
      url: "include.php",
      data: {user_two: user_id}
    }).done(function(data) {
       data = JSON.parse(data);
       if(data.msg) {
        //everything is ok
        $("#follow"+user_id).hide();
        $("#unfollow"+user_id).show();
       } else {
         //handle the error
       }
    )}
 });

PHP part:

<?php

include('db.php');
$user_two = $_POST['user_two'];
$query = $handler->query("INSERT INTO follow (user_one,user_two) VALUES ('1','$user_two')");
if($query) { //check if query ran successfully
 echo json_encode(array("msg" => 1)); 1 for success
} else {
 echo json_encode(array("msg" => 2)); 2 for error
}
?>

As for the "what is return false in ajax": .follow -> targets an tag. Clicking on an a tag makes your browser navigate to the url specified in href="". return false disables this behaviour as you don't need the page to refresh or go to another page :)