Labels are used to categorize your contacts/conversations and create more visibility within your account.
Once you have set up your labels, you can start applying them to your contacts.
You can apply the label in different situations:
add the label manually from the Contacts page:
add the label manually from the Messenger page:
add the automatic default label to all incoming conversations, which can be set in Labels Setting.
add the label from the campaign:
Moreover, you can filter by labels on Messenger and Contacts page: