Go to SETUP > MARKETING > REFERRALS
This is a mandatory field as part of the booking process. You can ask your customer how they heard about you eg. through a Google search, the local magazine or if they have been before. You can have as many referral options as you like.
Tip: You can see a pie chart of referral statistics (by month or year) on the dashboard and you can also generate a report of your referral options to see where your marketing really works!