Tags
Manage the team's tags from Settings.
Settings > Tags lists every tag, split into a Shared tab and a Private tab: shared tags are set up by an administrator and available to the whole team, private ones are yours alone.

Go to Settings > Tags.
Select New tag.
Enter a name, choose a colour, and choose whether it's shared or private.
Select Save.
Apply a tag to a conversation from the tag control inside it. Select the same tag again to remove it.