There are three ways you can apply a tag to a tenancy:

Tenancy Wizard

Tags can be applied as you are creating a new tenancy through the Tenancy Wizard.  The Details section on the first screen of the wizard contains a tags field. Entering one or more letters will display a list of any matching existing tags.  If the tag you are after doesn't exist, continue typing to create and apply the new tag. 

Once the tenancy is created, the applied tags are visible on the Tenancies screen.

Commercial Tenancy Wizard

Residential Tenancy Wizard

Import a Tenancy

A column has been included on the import tenancy template to add tags to each tenancy.  Enter all tags for each tenancy in the Tags column, separating each tag with a comma.

Tenancy Details

Tags can also be applied or removed to existing tenancies from the Tenancy Details tab.