Q:

How can I add a custom button by using a custom module in Magento 2.3?

I wanted to add my own button in the Shopping Cart as I tried to show you in the screenshot.

But I didn't find a tutorial that worked for me. Do you have any idea how I can do this? (I want to make my own extension)
(EDIT) This is what I have done so far:
In the registration.php file:
<?php
  \Magento\Framework\Component\ComponentRegistrar::register(
    \Magento\Framework\Component\ComponentRegistrar::MODULE,
    'Vendor_ModuleName',
    __DIR__
 );

In the module.xml file:
<?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="Vendor_ModuleName" setup_version="1.0.0"></module>
</config>

In the Button.php file:
<?php
namespace Vendor\ModuleName\Block;
class Button extends \Magento\Framework\View\Element\Template
{
    public function __construct(
        \Magento\Backend\Block\Template\Context $context,
        array $data = []
    ) {
        parent::__construct($context, $data);
    }

}

In the checkout_cart_index.xml file:
<?xml version="1.0"?>
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
        <referenceContainer name="cart.summary">
                <block class="Vendor\Module\Block\Button" after="-" name="custom_button" template="Vendor_ModuleName::button.phtml" />
        </referenceContainer>
</page>

In the button.phtml file:
<button>Your Button</button>

I also ran all commands you have told me.

A:

Create a Custom Module as Follows

Vendor\ModuleName\registration.php

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

then

Vendor\ModuleName\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="Vendor_ModuleName" setup_version="1.0.0">
       <sequence>
            <module name="Magento_Checkout"/>
       </sequence>
    </module>
</config>

After that run following Command
php bin/magento setup:upgrade
php bin/magento setup:di:compile
php bin/magento setup:static-content:deploy -f
chmod -R 777 var/ pub/ generated/

Add this is Your

Vendor\ModuleName\view\frontend\layout\checkout_cart_index.xml

<?xml version="1.0"?>
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
        <referenceContainer name="cart.summary">
                <block class="Vendor\Module\Block\Button" after="-" name="custom_button" template="Vendor_ModuleName::button.phtml" />
        </referenceContainer>
</page>

Now in 

Vendor\ModuleName\Block\Button.php

namespace Vendor\ModuleName\Block;
class Button extends \Magento\Framework\View\Element\Template
{
    public function __construct(
        \Magento\Backend\Block\Template\Context $context,
        array $data = []
    ) {
        parent::__construct($context, $data);
    }

}

then in

Vendor\ModuleName\view\frontend\templates\button.phtml

<button>Your Button</button>

