Discount Add-On Coding Help

[terriwarren 0]

I downloaded and installed the ot_discount add on for osCommerce 2.3.4.1. I am having a great deal of difficulty figuring out the coding for this. I believe I edited the title page correctly, since I just wanted to call it 15% discount.

But I am having a lot of trouble figuring out the codes for the other pages:

catalog/admin/discount_codes
catalog/includes/modules/order_total/ot_discount

I know that the file catalog/admin/includes/languages/english/discount_codes gives some of the formatting, but it is still a little confusing with all the other coding on the pages. I know since I want to include all customers and all items, I need to leave those fields blank. 

As you can see, I am not very experienced with php coding. What I want is to create a discount code for 15% off the total. My site does not charge sales tax. And I use PayPal for all payments.

Can someone please help me understand this coding? I have been trying for a while now. I would appreciate a point in the right direction.