The Showcase theme is available in 4 styles - Beard, Betty, Luna and Native. These demo stores aim to illustrate the variety of looks possible with the theme. Choose your theme style in the Theme Settings tab. The style settings will affect cross store elements such as your fonts, cart behaviour and social media icons.
Applying a theme style will overwrite any existing settings in your Theme Settings tab. Your section specific settings won't be affected. More information about theme styles can be found in this Shopify article.
Add links to your social media pages under Theme Settings > Social Media. If you wish to link to an social network that isn't listed, then you can add your own icon using the custom link option. Links can be shown in the footer in a text block. To add your links, simply choose a text block and select 'Show social media links'.