New Inbox Styles for GmailClassic : Shows your most recent messages at the top of your inbox
Important First : Only important messages appears on top (including reads and unread messages)
Unread first: Puts all unread messages at the top of your inbox ; everything else at the bottom
Starred First : Starred messages appear at the top; everything else at the bottom
Priority Inbox : Important and unread messages appears on top, then starred messages and then everything else.
You can choose any style from tabs at the top of your inbox and use it for a week, then those tabs will go away. You can always switch back to your inbox style anytime by selecting it from Inbox labels’ drop down menu.