How to Add a Label to a Gmail Message
Folder-based sorting stores emails in one location. Label-based sorting can apply several labels to a single message. To add one or more labels to Gmail messages:
How to Customize Your Gmail Labels
The Label As dialog box includes a link to Manage Labels, which is a shortcut to the Labels screen of the Gmail Settings menu. Either click that link, or go to Settings > Labels, or (if you’re logged in to your Gmail account) use this shortcut link: At the bottom of the settings screen, you’ll see your custom labels. Select Create New Label to add a new label to the list. Each label supports four settings groups:
Show in label list: Anytime a list of messages with labels appears in the left sidebar, select show (the default) to show the label persistently, hide to suppress it persistently, or show if unread to appear only when unread messages with that label appear. Show in message list: Select whether the label appears on messages in the message list. Actions: Select Remove to delete the label or edit to change it. Show in IMAP: Force email programs (like Microsoft Outlook) that use IMAP folders instead of Gmail labels to treat labels like IMAP folders.
How to Manage Gmail Labels
To edit or delete Gmail labels: