Click on Config, will be redirected to OMSConfig page where you can see two tabs like "Pay Method" & "Coupon Code".
In "Pay Method" tab you can add new pay methods by clicking on "Add New pay method" button.
In "Coupon Code" tab you can add coupon code ,by clicking on "Add New Coupon Code" button will get a popup window where you can create coupon by giving start and end date with name and discount.
After filling all the above mentioned fileds click on add then it will be added.