The social sharing icon on your deals page allows visitors to tell others about the deals you are offering. To prepopulate the text with something from the page, add a Meta Description. 

Start by clicking Online Store > Pages and open the Deals page. Scroll down and you will see the Meta Description field. Write a quick description in the field and click Save. 

You have now updated the meta data on the page and the social sharing button picks up the text like so: