Turtle Wax currently has a 20% off car cleaning kits promotion as the main offer, with discounts already applied on kit product pages. That 20% off deal is best for you if you are buying a kit rather than individual accessories, because the discount only applies to kits. There is also a separate range of car cleaning accessories from $3, with prices already marked down on those product pages.
Small spend on accessories: If you want a single cheap item, use the accessories range that starts at $3. Those items are priced as marked on the product pages, so your saving is the difference between full price and the shown price. For example, an accessory marked $3 costs $3 at checkout with no code needed, and the 20% kit discount does not apply to accessories.
Buying a single kit: The 20% off kits applies automatically on kit pages. On a $50 kit, for example, the price shown will already reflect 20% off, so you pay $40, a $10 saving (original $50, percent 20%, final $40, saving $10). On a $120 kit, the shown price will be $96, a $24 saving (original $120, percent 20%, final $96, saving $24).
Buying multiple kits or a high value kit purchase: The 20% off is the same rate regardless of basket size, so it scales with the total kit value. If you plan to buy several kits, the best route is to add the kits to your cart and use the product pages that already show 20% off, because no further checkout code is required and the discount will apply to the kits shown as eligible.
Mix of kits and accessories: Kits get 20% off automatically. Accessories are priced as marked and do not qualify for the kit discount under the offer terms. When your cart contains both, the kits will reflect 20% off and the accessories will charge their marked price, so compare the totals shown at checkout to see the final amount.
Newsletter signup: Signing up may bring special offers and promotions in future, so if you are a first time customer and want potential extra discounts later, join the newsletter. The signup is not required to get the 20% off kits or the $3 accessories and does not replace those current prices.
Take whichever option leaves you with the lower total for the same items. The only combination rule stated is that kit prices are reduced for kits only and accessory prices are as marked, so compare the kit adjusted total versus the accessories marked total and choose the items shown at their already reduced product page prices.