https://support.google.com/a/users/answer/9260550?hl=en
Create a label:
To top1. While logged in to your Gmail account, at the top right, click the “Settings” gear icon and then click “See all settings”.
2. Click the “Labels” tab.
3. Scroll to the Labels section at the very bottom and click “Create new label”.
4. Enter the label name and click Create.
5. You can also create nested labels, which are like subfolders.
Add a filter and easily apply a label
To top1. While logged in to your Gmail account In the search box at the top, click the “Down arrow “.
2. Enter your search criteria.
3. At the bottom of the search window, click Create filter.
4. Enter the words to filter under the “Has the words” input box
5. Click “Create filter”
6. In the next page, enable “Apply the label” and choose the label you’ve previously created
7. Scroll down and enable “Also apply filter to matching conversation”
8. Click “Create filter” and wait for the changes to take effect.
Apply a color to a label:
To top1. In the left panel, point to a label and click More (three dots).
2. Point to Label color and choose a color. Or, click Add custom color. The change instantly applies to all email with that label.
