I don't know if I truly understand what it is
It just handles your email a little differently than, say, Gmail....there's automatic grouping, so any of my email newsletters are lumped together or emails from job search sites are put together...and then you can click to expand and see them all....it's not just one long list of emails like a traditional inbox.
You can also "snooze" emails you don't want to deal with right away....If I get a save-the-date email for something a month out, I can snooze it for 3 weeks, it will disappear from the inbox and then pop back up a week before the event. Also if I set a reminder in Google Now it will show up in my inbox.
It's just a clean nice looking and easy interface. Though I have heard that people who have several consolidated email accounts (work, school, personal, etc) didn't like it as much. But it's not like you have to keep it if you don't like it....try it out and see if it works for you.