In Gmail generally if you don’t read a message then that message will appear in bold color in inbox reminding that you have not yet opened or read the message, ofcourse we can mark it as read from choosing more actions.

But sometimes we tend to forget to read the emails and hence there will be bulk of unread messages stored in your inbox if you want to find all unread messages in Gmail

In gmail  in the search box type label:unread label:unread and click Serach Mail as Gmail shows all unread messages.

unread messages in Gmail