It means that the certificate covers the offspring until they are one year old. They will need their first CAE test along with the rest of the herd at one year old and it needs to be done annually.
Most shows, breeders etc will not want you taking your goats there without certificated proof of whole herd negative status. It entails a quick blood test by the vet who then send it off to a lab. There is a form on the BGS website that you can download and ask the vet to send along with the form so the results are presented universally.
In order to produce good quality kids, you are more likely to need a good vaccination/worming/dietry/socialisation programme than testing I think. We had one of ours tested for Johnnes (?sp) but only because she was poorly. CAE is the main one. Oh and make sure any billies you use are CAE tested too!