What is a Health Certificate?? ?

I'm signing up for 4-H because a guy from my church asked me if I wanted to show his horses at the fair.(I'm buying his Paint mare) I said sure,so now I'm joining,but there's this part that says I'm going to need a Health Certificate for the show. I SHOULD know what it is,but I don't! Is it the same thing as a Coggins or no? If it has to do with Vaccinations I was planning on vaccinating Rosie against EEE,WEE,Tet and Potomac Horse Fever myself (No mean comments,I know what I'm doing) and let the vet do Rabies and West Nile. So what exactly is it,and will I be able to get one if I vaccinate against EEE,WEE,Tet and Potomac myself? Also,what's the cost of a Health Certificate in your area?(I'm in Iowa) Thanks!!