First, click the 'Share' button located in the Editor toolbar or in the shortcuts menu from the dashboard thumbnails.
Next, ensure there is public access to your URL, as shown below.
Note that if you upload a Piktochart image (jpeg or png file of your visual) to Facebook, it will shrink automatically to fit dimensions set by Facebook. Including the URL in the body of your Facebook post would allow your audience to view the visual on our page, where it renders better. Facebook, Twitter, Google+ and LinkedIn icons are located in the general icon collection in the editor. Use our search function to locate the one you want.
Additional ideas and tips for sharing Piktochart visuals on Social Media can be found in this blog article. It sheds some light on best practices, and is full of practical advice, including an up-to-date listing of social media image dimensions (so that your Piktochart creations are always the right size). Get creative!