Google is slowly rolling out the new inbox with automatic sorting
Gmail's new tabbed inbox should be available to most people by now. While Gmail is still rolling out slowly; you may already have it available even if you haven't noticed.Google will notify all users that the feature is available to them eventually, but you can check to see if it's available to you by clicking on the "gear" button and see if the entry "Configure inbox" is available.
If it is, you can switch over to the new organized inbox. Your email has already been sorted and placed in the appropriate inbox tab, but you can choose the tabs you want displayed by default.
There are only five options for now: primary, which displays the important messages, and social for stuff from Twitter, Facebook, YouTube and so on.
Then, the promotions tab is for offers, newsletters and such; updates for bills and receipts, and finally forums for messages from online news groups and, well, forums.
When the new inbox works, it's actually a great way of keeping everything sorted and focusing on the stuff you want to focus on at any given time.
You can actually help it get better by moving messages to the tab you think they belong to if Google messes up, you can simply drag and drop the message to the right place.
The sorting should also get better in time as Google refines its filters and algorithms.
However, if you don't find the new inbox useful or just don't like it, you can revert to the inbox you were using before quite easily. Gmail offers several inbox types and users can switch between them.
To go back to your old inbox style or to choose between the several available, go to the "gear" menu button, select Settings > Inbox tab and pick the inbox type you want from there.