Some Stockholm demos load some content into your footer such as Social Link icons. You can edit each footer column under Appearance > Customize by expanding the Widgets panel.
Stockholm's demo social icons are displayed using a Text widget and a Select shortcode. You can edit the link for each one shown and click Save changes to use the demo setup.
If you wanted to change the icons or add/remove one, you must create a new draft post, then click the blue S icon to access the shortcode list.
1. Choose Social Icons at the bottom and a little settings window will appear.
2. Choose Circle, then select the social network from the Font Awesome drop-down.
3. Choose Small from the size drop-down.
4. Enter your profile url in the Link field
5. Choose Blank from the Target drop-down
6. Choose your colors and click Submit.
7. Repeat for the other icons you want to show.
8. When done, you will have a big block of code in the post editor. Copy the whole thing.
9. Return to the Appearance > Customize screen and go back into Widgets > Footer Widget 1
10. Delete the existing code from the Text widget, then paste your new code there and click Save Changes