You may not use Facebook or Twitter yourself, but many people do, and what they share is up to them. Open Graph metadata is also used by other social networks, such as LinkedIn.
Whilst you cannot control what people share, if you have a SimDif Smart or Pro site, you can control how your site is seen when people do share it.
Tap on the 'G' icon at the top of the page, fill in the fields in the Facebook and Twitter tabs, then ‘Apply’ and ‘Publish’.
If you set a different Title, description and image for each page of your site, each page will be seen as unique when it is shared