To create a mix and match discount (e.g. Buy One Get One Free) you will need to follow these steps:
1. Log into the back office.
2. Go to products and items, then go to discounts.
3. Using the tabs up top select a mix and match discount.
4. Hit the add new discount button.
5.  Add the name, what menu items it includes, if the discount applies before or after taxes, set the percentage and how many of those items you nee to buy to get the discount.
6. Click update and publish.
BOGO Example (Click Image To Open In New Tab):