GMail has different inbox type such as Classic, Important first, Unread first, Starred first and Priority Inbox.
Classic :- This is the old way of display mails i.e all the recent messages will be displayed at the top of the Inbox.
Important first :- This display the emails from the contact whom you have interacted at the top of the Inbox.
Unread first :- This would display all the unread emails at the top of the Inbox.
Starred first :- This would display all the starred emails at the top of the Inbox.
Priority Inbox :- This would prioritize the emails by combining important, unread and starred feature.
The default inbox type in GMail is set to Classic but users can change the default inbox type using the Mail Settings.
Click the Options icon and select Mail Settings from the list of menus.
In the Mail Settings page, click the Inbox tab and navigate to Inbox type section.
Set your desired Inbox type by selecting it from the drop down list. Click the Save Changes button available at the bottom of page. Now GMail will display the emails based on the selected Inbox type.