This article explains how to add a Mark As Read button to Gmail, which will help you to keep your Inbox folder organized and easy to manage.
By default, Gmail does not provide any option to mark unread messages as read, so here's how to remedy to this situation:
Connect to your Gmail account, click on the cog menu located at the top right corner of your screen and select Settings. Navigate to the Labs tab and search for the Mark as Read button lab by Mark K. Select Enabled:
Scroll to the bottom of the page and click on Save Changes.
You can test out this new feature by going to your Inbox and selecting a few messages (by ticking their corresponding checkboxes).Click on the Mark as Read button that now appears next to the Delete button: