How to create custom module in magento 2

To create Hello World module, you need to complete the following high-level steps:

Step 1: Create the folder of Hello World module

app/code/A/HelloWorld
Step 2: Create etc/module.xml file

app/code/A/HelloWorld/etc/module.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
    <module name="A_HelloWorld" setup_version="1.0.0">
    </module>
</config>

Step 3: Create etc/registration.php file

<?php
\Magento\Framework\Component\ComponentRegistrar::register(
    \Magento\Framework\Component\ComponentRegistrar::MODULE,
    'A_HelloWorld',
    __DIR__
);

Step 4: Enable the module

php bin/magento module:status

You should see the module is disable now:

Follow exact guide to enable the module right now, let run the command as:

php bin/magento module:enable A_HelloWorld

Your module should be available now.

After this step, when you open your website in browser you will get an error saying

Please upgrade your database: Run “bin/magento setup:upgrade” from the Magento root directory.

Let run the command:

php bin/magento setup:upgrade

Finally the fold like this: