In short: Add a 15% Product Discount, an Order Discount of Fixed Amount 10 with Cart Subtotal at least 100, and a Shipping Discount with Free Shipping. One code gives all three.
Why one code: Shopify's own discount codes each hold one kind of discount, so this offer would take three codes, entered together. In OneCode: Stackable Discounts it's one code, and every part of it applies whenever its conditions are met.
Steps
Click Create discount and enter a code, for example
TREAT15.Click Add Discount Type and enter
15in Percentage. Keep Target as All Products.Click Add Discount Type and set Discount Type to Order Discount. Set Value Type to Fixed Amount and enter
10.In the order discount, under Per-Discount Conditions, click Add Condition. Set Field to Cart Subtotal, Operator to Greater than or equal to and Value to
100.Click Add Discount Type, set Discount Type to Shipping Discount and keep Free Shipping.
Click Save discount.
What the customer gets
$120 cart: 15% off the items ($18), then $10 off the order, so the customer pays $92, with free shipping.
$60 cart: 15% off the items ($9) and free shipping. No $10 off, because the cart is under $100.
Variations
Bigger reward for bigger orders: add a second order discount of
25with Cart Subtotal at least200. Only the biggest order discount that qualifies is used, so a $250 cart gets $25 off, not $35.Free shipping from $75 only: give the shipping discount the condition Cart Subtotal at least
75.Percentage off the order instead: set the order discount's Value Type to Percentage, for example an extra 5% off orders over $100.
Good to know
Shopify takes order discounts off after product discounts, so the $10 comes off the already-discounted total.
Cart Subtotal is measured before discounts. A $110 cart still gets the $10 off, even though it's $93.50 after the 15%.
The parts of one OneCode discount always work together. Combinations only matters for your other, separate discounts. See How OneCode discounts combine with your other discounts.