Show social media link icons
To include linked icons for social media accounts, first confirm that the correct URLs have been added to the Social media portion of the Theme settings:
Customize > Theme settings > Social media
Once these have been added and saved, icons will show in the footer as long as the primary footer is activated (as opposed to the secondary Alternate footer).
Display payment icons
To show payment icons, first navigate to the Footer section in the theme editor:
Customize > Sections > Footer > Payment icons
Enable Show payment icons. You'll set and manage these from your Shopify admin under Settings > Payments. You can find more information about that here.