How do I add a promotional Code field in my checkout form ?

[kifah_Mas]

Hello,

 

Please help me, I am trying to add a promotional code field in my checkout order page, I want my customers to enter a code somewhere in the order process so they can get a $10 discount.....I dunno how to do this, where can i go to add this field ?

 

I really appreciate any response from you..

 

Thank you :roll: