Go to Woocommerce > Discount Rules in your dashboard.

Click ADD NEW RULE button to add a new Rule Setting.

Once you have finished setting up the rules, click the SAVE & CLOSE button.

Example: Buy 2 get 1 for Free (Selected Category).

When 2 products of the same category are in the cart then the cheapest product in the cart will be provided a discount.

RULES SETTING: