How can I exclude / ignore certain parts of the content text?

By default, WPSSO will use the excerpt for the various description values. If an excerpt isn’t available, the post content text will be used instead. If there are parts of your content text that you don’t want the plugin to see, you can wrap those sections between <!--wpsso-ignore--> and <!--/wpsso-ignore--> comment tags. If your content is generated from plugin templates (ecommerce or gallery plugins, for example), the ignore tags would probably go in those templates.