add_action('wp_dashboard_setup', 'custom_dashboard_widgets');
function custom_dashboard_widgets(){
//first parameter is the ID of the widget (the div holding the widget will have that ID)
//second parameter is title (shown in the header of the widget) -> see picture bellow
//third parameter is the function name we are calling to get the content of our widget
wp_add_dashboard_widget('my_custom_widget_id', 'My Widget Title', 'my_custom_widget');
}
function my_custom_widget() {
//the content of our custom widget
echo '<p>The content of the widget goes here.</p>';
}