The new default categories, based on Gmail's existing Label system, are Primary, Social, Promotions, Updates, and Forums. They appear as large tabs on the Gmail site, easy to use for touch screens and fully customizable. You can also drag-and-drop messages between them, and Google will automatically "learn" how you want them filtered.
It's not quite the "Card"-ification of Gmail, as Google has gone to great lengths to make as many of its services as possible take their visual cues from the popular "Card" layout of Google Now. However, it's definitely more touch-friendly and designed to make it easier to organize e-mail.
Whether it helps you achieve that elusive "inbox zero" remains to be seen, but it should go some distance to help keep the Gmail faithful from straying to more mobile-friendly mail clients likeMailbox.
The updated app for Android is expected soon. The iOS app will be available as soon as it is approved by Apple's App Store, Google said, and the Web-based update will be rolled out over the next few weeks. If you can't wait for the Web update, the Settings menu behind your Gear icon will soon have an option to "Configure Inbox." Choose "Default" and refresh the page to see the new look.
Once you have access to the new look, you can switch between it and older Gmail views using the drop-down menu that appears when you mouse over your inbox.