The field checkbox helps you to create a checkbox on the backend when editing a post (or post type) then show the value on the frontend with the helper function rwmb_meta(). You can create a condition to show something on the frontend if the box is checked on the backend.
$value = rwmb_meta( $field_id );
// If field is checked.
if ( $value ) {
echo 'Checked';
// Do something.
}
// If field is unchecked.
else {
echo 'Unchecked';
// Do something else.
}