You can add labels to your emails with a few different ways:
- Check the checkbox in Inbox next to the emails you want to label and click on the label icon
on the top toolbar. Check the labels you want to add and click Apply
- After opening an email follow the click on the label icon
on the top toolbar. Check the labels you want to add and click Apply
- Drag the label from the left side panel on top of the email you want to add it to in Inbox.
You can also use labels as folders. Just drag the email on top of the label from Inbox. The message will get archived and can now be found under that label.