1) In the top of Gmail, click “Create Filter”.
2) In the “Has the words” field type some keyword, or email address (for to: from:).
3) Click “Test Search” to make sure you get an accurate list of the emails you’re hoping to find, then click “Next Step”.
4) Click the checkbox next to “Apply the Label”, then create ‘new label’ using the drop down, then type in a label name.
5) To add the label to emails you’ve already received simply check the box next to “Also apply filter to X conversations below”.
6) Finally, click “Update Filter”.
Google automatically tags incoming messages with a series of labels. You can create a enormous amount of actions using these tags in combination with filters, such as creating labels for unread message only, etc.
You can use shading or identifier tags next to each subject line in your inbox. You can use this feature to highlight messages from your boss, key clients, and various team members.