In continuation of Create Promotion, this article shows the specific details for BOGOF Promotion

As the name suggests, you can define the data set in a way that customers when add X item in their bag, they get the Y product for free. The data set section gives you option to define X and Y products.
To set this kind of promotion you need to save items in the Included and discounted dataset. Included Dataset, Products from Included items when added to bag customer will get item from Discounted Dataset, as shown below.