Hi Noor ul haq Abbasi,
Embedding the dashboard is the answer for your question. The Dashboards published to Tableau Public/Server can only be embedded.
Few videos are on Internet on how to embed them in your blogs/webpages.
Facebook & Twitter(I guess twitter too) doesn't allow you to embed your tableau dashboards
but you can export your dashboard to images and share on Facebook and Twitter. Or sharing the link there will take your audience to your Tableau Dashboard.