Has anyone used wordpress?

Has anyone used wordpress before? How can WordPress create a data table? If it can be created, is there any way to operate the created data table? I used the following code. It is said online that it can be used in a plug-in. But it didn’t work for me. I wrote the code wrong or put it in the wrong place
function wp_user_avatars_create_table() {

<code>global $wpdb;
$table_name = $wpdb->prefix . "test";
if($wpdb->get_var("SHOW TABLES LIKE '$table_name'") != $table_name){
     

    $sql = "CREATE TABLE IF NOT EXISTS " . $tablename . " (
          `test_id` int(8) unsigned NOT NULL,
          `test_name` varchar(200) CHARACTER SET utf8 NOT NULL,
          `test_password` varchar(200) CHARACTER SET utf8 NOT NULL
        ) ENGINE=MyISAM DEFAULT CHARSET=utf8;";
       
   dbDelta($sql);
}</code>

}

register_activation_hook( __FILE__,'wp_user_avatars_create_table');

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Has anyone used wordpress before? How can WordPress create a data table? If it can be created, is there any way to operate the created data table? I used the following code. It is said online that it can be used in a plug-in. But it didn’t work for me. I wrote the code wrong or put it in the wrong place
function wp_user_avatars_create_table() {

<code>global $wpdb;
$table_name = $wpdb->prefix . "test";
if($wpdb->get_var("SHOW TABLES LIKE '$table_name'") != $table_name){
     

    $sql = "CREATE TABLE IF NOT EXISTS " . $tablename . " (
          `test_id` int(8) unsigned NOT NULL,
          `test_name` varchar(200) CHARACTER SET utf8 NOT NULL,
          `test_password` varchar(200) CHARACTER SET utf8 NOT NULL
        ) ENGINE=MyISAM DEFAULT CHARSET=utf8;";
       
   dbDelta($sql);
}</code>

}

register_activation_hook( __FILE__,'wp_user_avatars_create_table');