The redesign is all about helping you hone in on your interests, without losing that random factor that made StumbleUpon what it is today. They’ve done this by adding Channels and a new Explore Box.
Channels are the StumbleUpon version of Facebook pages. They’re accounts from brands, celebrities and sites such as ESPN, Campbell’s Soup or Chelsea Handler. You can Follow a Channel, then Stumble it when you want to look through the suggested pages.