How to create a custom widget in WordPress?

// Creating the widget 
class ts91_widget extends WP_Widget 
{
 
 // The construct part  
 function __construct() 
 {
  //code goes here for widget name and description things
 }
   
 // Creating widget front-end
 public function widget( $args, $instance ) 
 {
  //code goes here for creating front end of widget
 }
           
 // Creating widget Backend 
 public function form( $instance ) 
 {
  //code goes here for creating backend stuff where you can use the form
 }
       
 // Updating widget replacing old instances with new
 public function update( $new_instance, $old_instance ) 
 {
  //code goes here to update the widget content.
 }
 
// Class ts91_widget ends here
}

//Registering the widget
function ts91_load_widget() 
{
    register_widget( 'ts91_widget' );
}
add_action( 'widgets_init', 'ts91_load_widget' );

// Creating the widget 
class ts91_widget extends WP_Widget 
{
 
 // The construct part  
 function __construct() 
 {
  parent::__construct(
  
  // Base ID of your widget
  'ts91_widget', 
    
  // Widget name will appear in UI
  __('91 TechSquare Widget', 'ts91_widget_domain'), 
    
  // Widget description
  array( 'description' => __( 'custom widget based on 91 TechSquare Tutorial', 'ts91_widget_domain' ), ) 
  );
 }
   
 // Creating widget front-end
 public function widget( $args, $instance ) 
 {
  $title = apply_filters( 'widget_title', $instance['title'] );
  
  // before and after widget arguments are defined by themes
  echo $args['before_widget'];
  if(empty($title))
  {
   $title = "91 TechSquare Widget Title";
  }
  if ( ! empty( $title ) )
  echo $args['before_title'] . $title . $args['after_title'];
    
  // This is where you run the code and display the output
  echo __( 'Hello Developers, Hope you are doing well!', 'ts91_widget_domain' );
  echo $args['after_widget'];
 }
           
 // Creating widget Backend 
 public function form( $instance ) 
 {
  if ( isset( $instance[ 'title' ] ) ) {
  $title = $instance[ 'title' ];
  }
  else {
  $title = __( '91 TechSquare Widget Title', 'ts91_widget_domain' );
  }
  // Widget admin form
  ?>
  <p>
  <label for="<?php echo $this->get_field_id( 'title' ); ?>"><?php _e( 'Title:' ); ?></label> 
  <input class="widefat" id="<?php echo $this->get_field_id( 'title' ); ?>" name="<?php echo $this->get_field_name( 'title' ); ?>" type="text" value="<?php echo esc_attr( $title ); ?>" />
  </p>
  <?php
 }
       
 // Updating widget replacing old instances with new
 public function update( $new_instance, $old_instance ) 
 {
  $instance = array();
  $instance['title'] = ( ! empty( $new_instance['title'] ) ) ? strip_tags( $new_instance['title'] ) : '';
  return $instance;
 }
 
// Class ts91_widget ends here
}

//Registering the widget
function ts91_load_widget() 
{
    register_widget( 'ts91_widget' );
}
add_action( 'widgets_init', 'ts91_load_widget' );