You can claim your Coupons via the 'Coupons' link at the top of TheMarket webpage.
Simply locate the Coupon you wish to use and select the 'Claim Coupon' button. This will automatically put the coupon into your checkout. Once you have completed shopping, proceed through to 'Checkout'.
Once you’re in the checkout screen for your item, click on ‘Select Coupon or Enter Code’ and select your coupons from the available option or enter your coupon code. The coupon amount will then be deducted from the payment total.