Each tier can have up to 10 rewards of two kinds:
One-time rewards: given once, when the customer reaches the tier. For example, a $20 gift card or one free product.
Permanent benefits: available on every order while the customer is in the tier. For example, 10% off every order or free shipping.
Rewards can be order discounts, product discounts, free shipping, free products or gift cards. Turn on "Keep unused one-time rewards available on next tiers" so customers don't lose rewards they haven't used yet.