How to set default values for configuration fields in Magento 2

Today we will learn how we can set the default values for our module’s configuration fields.
I am assuming that you have a good understanding Magento 2 directory structure .
So I will not be covering that you can read our Guide for this Magento 2 basic module.
I hope you must have read the above Guide.
Now let’s Start ,
Step 1 : create file in this location for creating configuration fields –
app/code/<vendor_name>/<module_name>/etc/adminhtml/system.xml

<?xml version="1.0"?>
<!-- /**
* Webkul Software.
*
* @category Webkul
* @package Webkul_Wkmodule
* @author Webkul
* @copyright Copyright (c) 2010-2017 Webkul Software Private Limited (https://webkul.com)
* @license https://store.webkul.com/license.html
*/ -->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Config:etc/system_file.xsd">
    <system>
      <section id="payment">
          <group id="wkmodule" translate="label" type="text" sortOrder="2" showInDefault="1" showInWebsite="1" showInStore="1">
              <label><![CDATA[Test Payment Module]]></label>                  
              <field id="active" translate="label" type="select" sortOrder="101" showInDefault="1" showInWebsite="1" showInStore="1">
                  <label>Enabled</label>
                  <source_model>Magento\Config\Model\Config\Source\Yesno</source_model>
              </field>
          </group>
      </section>
  </system>
</config>

Step 2 : Create file to set default values here :
app/code/<vendor_name>/<module_name>/etc/config.xml

<?xml version="1.0"?>
<!--
/**
* Webkul Software.
*
* @category  Webkul
* @package   Webkul_Wkmodule
* @author    Webkul
* @copyright Copyright (c) 2010-2017 Webkul Software Private Limited (https://webkul.com)
* @license   https://store.webkul.com/license.html
*/
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Store:etc/config.xsd">
    <default>
        <payment>
            <wkmodule>
                <active>0</active>
                <------>x</---->
            </wkmodule>
        </payment>
    </default>
</config>

Similarly, you can set the default values for the other fields as well.

Hope this blog may help.
If you want to add button in configuration so please follow this wonder full blog :
add Button in magento 2 configuration section .
If you have any Query then feel free to ask in below comment section.