If you want create a database table while a activating the plugin then you have to register_activation_hook() function. The following code can be placed in your main plugin file. The function will create tables in your Database.

function myplugin_install() {
    global $wpdb; 
    $table_name = $wpdb->prefix . "mytable";
    $db_version = '1.0';
    /**Execute the sql statement to create table**/
    $sql = "CREATE TABLE IF NOT EXISTS " . $table_name . " (
        `ID` int(11) NOT NULL AUTO_INCREMENT,
        `field1` varchar(300) DEFAULT NULL,
		`field2` varchar(300) DEFAULT NULL,
		`field3` varchar(300) DEFAULT NULL,
		`field4` varchar(300) DEFAULT NULL,
		`field5` varchar(300) DEFAULT NULL,
		 PRIMARY KEY (`ID`));"; 
    require_once(ABSPATH . 'wp-admin/includes/upgrade.php');
    dbDelta($sql);
    add_option( "db_version", '1.0' );  
}
// plugin activation hook
register_activation_hook(__FILE__,'myplugin_install');

Then activate your plugin.If already activated then reactivate the plugin. It automatically create table in your database. That’s it.

Have any doubt, then comment here!

There is no difference between wp_insert_user() and wp_create_user(). The entire source of wp_create_user() is given below

function wp_create_user($username, $password, $email = '') {
    $user_login = esc_sql( $username );
    $user_email = esc_sql( $email    );
    $user_pass = $password;

    $userdata = compact('user_login', 'user_email', 'user_pass');
    return wp_insert_user($userdata);
}

It just calls insert version almost immediately, basically a shorthand wrapper.