how detect form is submitted? I use Drupal 7 and the Webform module.

How can I know if a form is submitted or not? I need this to show either error messages or success message after form submission in form page.

I prefer not to write a module because I think it is unnecessary to write a module for a very small task.

Some more info to further explain my question:


I already know about the setting for Webform per form. This setting is located "Content > Webforms(tab) > Edit(your form) > Webform(tab) > Form settings" (where you can add the confirmation message or redirect to a Custom URL).
Actually I render my webform in my node--contact.tpl.php and I use the Webform Validation module for my form validations. And with the form_get_errors function I get errors and loop through them and show them. And if submission is successful I show form successful submission message. I just don't know how to detect whether form is submitted or not.
There a setting for Webform per form. This setting is located "Content > Webforms(tab) > Edit(your form) > Webform(tab) > Form settings". You can add the confirmation message or redirect to a Custom URL.