Add New Dashboard Widget

Add a new widget to the dashboard. Note, this will add the widget to the bottom of the page. If you want to try to move it to the top, check out the Codex page about dashboard widgets

add_action('wp_dashboard_setup', 'add_custom_dash_boxes');
function add_custom_dash_boxes() {
    wp_add_dashboard_widget( 
        'welcome_box',
        __( 'Welcome', 'myplugin_textdomain' ),
        'welcome_box_text'
    );
}
function welcome_box_text() {
    echo 'Custom welcome text here';
}