Three reward types
Free Shipping — Removes shipping cost above a threshold.
Discount — % off or $ off the cart subtotal above a threshold.
Free Gift — Adds a chosen product at $0 above a threshold.
Steps
Open Cart Editor → Rewards → Add tier.
Pick the reward type.
Set the goal amount (cart subtotal in your store currency).
Pick the product (free-gift only).
Customize messaging — locked, unlocked, and "X more to unlock".
Recommended starting setup
If this is your first reward tier, start with Free Shipping at a threshold ~30% above your average order value. It's the easiest reward to test and customers respond strongly to it.