Buy the order as a regular item. Pay it about  the shopping card. After you pay it you get an email with an code. You should get this email within 24h. You, or a other person you like, can use the code at www.think-pink-celle.de.
After you finish your regular order you pay the order about the shopping card. There is a special payment option for the voucher code. Use the code and finish the order. 
If your order is higher than the value from the voucher you have to pay the different with an other payment option you like.
If the order is lower than the value from voucher you can use the different for the next order.
If it is a present contact us. Than you can get an email where you can print the voucher with code and if you like the value of the voucher.