Think of it as the first upload of product information that sets the foundation of your fields and data set. Every column in your Master CSV that contains data will create that field in your account. Any field with data that is not mapped to a Shotfarm Core Field will create a Custom Field. Fields with no data will be ignored. You can't turn on and off fields in your Master CSV so don't include fields with data that you don't want uploaded to your Shotfarm account.
Download an Example Master Data CSV: