A Webring is a loop or chain of websites connected together that you can easily browse through. Surfle has a few modes:
Surfle Mode - Browse through any official Surfle Webring. Overtime, additional Webrings will be added and you can change to a different one from the Settings page (click on the settings cog wheel icon at the top right of the extension's main popup).
Bookmarks Mode - Any of your own bookmarks folders can be selected as the list of websites you browse through.
Either mode can be surfed in order or you can check off Random Mode for a random experience.
