How can I add a section for special promo code that will enable a person to get a discount

Which features do you need? Please provide us more details about the features that you want to use. 

Sorry, by mistake I hit the send before typing the questions.
A. How can I add a section for special promo code that will enable a person to get a discount?
B. Is it possible to create a button that allows people to pay by check through mailing it, without going into PP for CC payment.
Thank you in advance,
RCS
...

It is possible to add Coupon Code to Payment Forms. Inside of this guide, you can find how to do it:

How to Add Coupon Code to Payment Forms

It is also possible to create multiple payment form. Please check this guide:

How to Create a Basic Multiple Payment Form

Feel free to contact us if you have any other questions.