Freebies are items in a booth that the seller agrees to give away, usually for promotional reasons. Sellers set freebie rules according to the quantity of items sold. You can set up item freebies under the Discounts & coupons page in the Edit booth options area (Selling > Booth settings > Discounts & coupons). A seller can agree to give buyers one freebie after buying one item, unlimited freebies after buying one item, or unlimited freebies without buying anything.
Once you've specified your freebie rules in your booth settings, you can indicate which items are freebies on the item listing page. Scroll to the pricing section, then select the "Item is a freebie" option and save the changes. Buyers will then be able to add your freebies to their cart according to the rules you set in your booth settings.