Drupal 8 Creating custom Block steps

Costume Module file structure (My Drupal version 8.1.2)

1. Create a folder under ‘/modules/’ for this explanation I am creating a ‘sampleblk’ (this is our module folder) folder inside module folder

2. Create module info file ‘sampleblk.info.yml’ inside sampleblk folder

name: Sample Block
type: module
description: 'Example Block for Drupal 8.'
package: Custom
version: 8.x
core: 8.x
dependencies:
  - node
  - block

3. Create sampleblk.module inside sampleblk folder

<?php
/**
 * @file
 */
?>

4. Create src folder and create Plugin folder inside ‘src’ and create Block folder inside ‘src\Plugin\’ folder and create SampleblkBlock.php filde (full path : modules\sampleblk\src\Plugin\Block\SampleblkBlock.php)

<?php

/**
 * @file
 */
namespace Drupal\sampleblk\Plugin\Block;

use Drupal\Core\Block\BlockBase;

/**
 * Provides a 'Hello' Block
 * @Block(
 * id = "sample_block",
 * admin_label = @Translation("Sample block"),
 * )
 */
class SampleblkBlock extends BlockBase {
	/**
	 *
	 * {@inheritdoc}
	 *
	 */
	public function build() {
		return array (
			'#type' => 'markup',
      		'#markup' => 'This is sample Block content.',
		);
	}
}

?>

Here in the comment section adding some annotation @block don’t remove it  it is required. Read more about annotation

1. ‘id’  = This property in the annotation defines the unique, machine readable ID of your block.

2. ‘admin_label’  = This annotation defines the human readable name of the block that will be used when displaying your block in the admin interface.

5. Install the new module from admin

6. clear the cache

7. Add your new block (I am just adding the new block to sidebar)

8. Check the effect

Github : https://github.com/bikeshm/drupal-8-block-sample1

Check this post alos : https://wiki.workassis.com/drupal-8-creating-custom-module-from-scratch/