Attributes are a way to tag reservations that can later on be used to retrieve them in the booking search page. To create a new attribute go to Configurations > Attributes. An attribute is just a label to be bound to a reservation, so it only needs to be defined using a mnemonic text:


Once defined, an attribute can be assigned to a reservation, using the specific box:


And, more interestingly, it will be searchable from the "advanced options" part of the booking search interface:

adavnced options