One of the new features to Discover is that there'll now be topic headers that allow for exploring topics. Your interests are now front and center, and are culled from your Google search results over time. So, for example, if your hobby is hiking, you'll see "hiking" show up as a new topic in Discover. Tap it, and it'll bring up a special topic page that list a slew of results that are focused on hiking, such as suggestions of nearby hiking locales and tips and tricks on how to explore a particular area. Some of these search results might be a few years old, but they're surfaced anyway because they're "new to you," according to Google.
The Discover page presents your interests in topic cards, just as it did before in Feed. Except this time, there'll be a control icon on the bottom right. Tap that, and you can decide if you want to see More or Less of that particular topic.
There'll be multilingual support for English and Spanish content -- you can even see both languages in one feed if you happen to speak both. Support for more languages is coming soon. The new Discover will roll out not just to the Google app, but also to the mobile homepage of google.com over the next few weeks.