These are called dashboard widgets. codex have documentation on this. Here is an example :
/**
* Add a widget to the dashboard.
*
* This function is hooked into the 'wp_dashboard_setup' action below.
*/
function example_add_dashboard_widgets() {
wp_add_dashboard_widget(
'example_dashboard_widget', // Widget slug.
'Example Dashboard Widget', // Title.
'example_dashboard_widget_function' // Display function.
);
}
add_action( 'wp_dashboard_setup', 'example_add_dashboard_widgets' );
/**
* Create the function to output the contents of our Dashboard Widget.
*/
function example_dashboard_widget_function() {
// Display whatever it is you want to show.
echo "Hello World, I'm a great Dashboard Widget";
}
For more check out : https://codex.wordpress.org/Dashboard_Widgets_API