How do I setup certificate for a course?? Anyway to set up a per month price?

I have figured out everything else about setting up courses except certificate, and if I can assign a course to multiple categories (But I figured I could find out about category once I enter more than one category, but certificate is another matter)
I have found where to create certificate, but I have no idea how I can connect the certificate to a course, and deliver it at the end. Is there any way to have its option, just as we have options to add text, image, question, when we are creating the units and place it on the last Unit, that way students can print it, upon meeting all the requirement.

Is there any way that I can set up a per month using marketpress. For example, If I set up the course to be for six months, would I be able to offer price at 100/month??

Please let me know.