Move a Message to a Label
Here’s how to move an email to a label (and remove the message from the current view) in Gmail:
Open Gmail and go to your Inbox or another view. Hover over the message you want to move. To the left of the message, select the handle (the double-dotted, vertical lines). To move multiple messages, make sure they’re all checked, then drag the handle for any selected message. Drag the message into the left panel, and place it on top of the desired label. If you don’t see all available labels in the left panel, hover the message over the label section. Each label is highlighted as you hover the message over it. Or, select More to see additional options. When the message is over the desired label, and the label is highlighted, release the handle.
Apply Custom Labels
You can use the same method as above to apply a custom label to a Gmail message. Make sure the label is visible in the left panel before you move the message. If the label isn’t visible, select More to find it.