Creating the discount
Step 1 - Open your store's Discounts page and click Create discount
Step 2 - Scroll down to the Discount Kit section, which should now be available, and click Gift with purchase
Step 3 - Fill in the desired settings and click Save
Storefront components
Automatic Gifts - Open your store's theme editor. Select App embeds in the left hand panel and then enable Core from Discount Kit. Open up Core's settings using the drop-down arrow and select Automatically add single variant gift products to the cart. In most cases, it's also best to enable Refresh page after making cart changes so that customer's carts do not become out of sync with the store's theme.
Once enabled, once a customer has unlocked a Gift with Purchase discount tier that contains a single product variant it will automatically be added to the cart. For gift tiers that contain multiple variants and the customer needs to choose from among them see instructions for enabling the Gift Selector below.
Gift Selector - Enable Core as above (Core is required for all storefront gifting functionality). Then enable the Gift Selector app embed found below Core. Feel free to customize the settings to your liking!