The coupons you redeem can be used to off set your purchases of mining contracts.
To do so,
Step 1. Login to your Hashnest account at www.hashnest.com.
Step 2. Check your coupons at "My coupons” the side bar.
Step 3. Then go to "Hash", choose the mining contrct you would like to purchase and place your order.
Step 4. Choose your preferred payment method and from your coupons.
Step 5. Click “Submit” to confirm your order.
Final step. Wait for your hashrates to be allocated to you and enjoy your mining!