function wp_handle_upload

Could someone point me to an example using wp_handle_upload. I’m tring to use it in my plugin to upload an image and I’m getting an error:
Invalid form submission.

This is my code:

if ($_POST['Submit']=='upload') {

include_once(ABSPATH . 'wp-admin/includes/media.php');
include_once(ABSPATH . 'wp-admin/includes/file.php');
$My_file = wp_handle_upload($_FILES[$_POST[image]]);

echo $My_file[error];
}