“I recently switched from Outlook Express to Gmail. Is there any way to sort my Gmail so that I can view unread messages only? It’s confusing to see a mix a read and unread messages in my Gmail inbox.”
Gmail offers many mail sorting options you can’t get with a traditional email client, but sometimes that comes at the expense of things we are used to. You can filter by unread messages in your inbox, but it takes a little advanced search technique.

Sorting Unread Inbox Messages
The Gmail search feature supports a bunch of special operators to specify message location, message read status, and a number of other useful characteristics. To make these operators useful, sometime you need to combine them in the Gmail search box. For viewing unread messages in your inbox, you need to use the combination in:inbox is:unread. This tells Gmail to show you only mail in your inbox with the unread status.

Sorting Unread Label Messages
The same trick also works for mail automatically filtered to a label. For labels you can use either in:label-name or label:label-name in combination with the is:unread designation. If the label contains more than one word it’s important to put a dash between each word.