From EGEE-see WIki

Obtaining Certificates

Some countries have their own CA, listed at Certified CA in SEEGRID Region, from which you will receive specific details about registration procedure in your country.

If your country does not have its own CA, use catch-all SEEGrid CA, following the general registration procedure described at How to request a certificate and http://www.grid.auth.gr/pki/seegrid-ca/documents/

However, the actual certification procedure is slightly different than described at above links. After generating a certificate request using your account on a SEE-GRID User Interface (UI) computer, send it to the RA for your country, together with your phone number, address, institution and e-mail at an academic or SEE-GRID affiliated institution. Country RAs are listed at http://www.grid.auth.gr/pki/seegrid-ca/ra/

VO Membership

After obtaining your certificate and sending acceptance email, register as a member of SEEGRID VO at https://voms.irb.hr:8443/voms/seegrid/webui/request/user/create