If the application did not come with an uninstaller application (few do, but those that do have uninstallers include e.g. Microsoft Office) - then all you have to do is quit the application, then drag it to trash from your applications folder or where ever you keep the applications. Empty the trash and that's it.
There are a few things this may leave such as a preferences file. Normally those files are very small and harmless so no need to find them separately.