To get any SSL Certificate you will need to pass validation process and provide a Certificate Signing Request (CSR). To Generate CSR, you can do it manually on your server using one of the instructions as below for the SSL vendor you have purchased accordingly :
Symantec SSL
https://knowledge.verisign.com/support/ssl-certificates-support/index?page=content&id=AR235
GeoTrust SSL
http://www.geotrust.com/support/generate-csr/
Comodo SSL
https://support.comodo.com/index.php?_m=knowledgebase&_a=view&parentcategoryid=33&pcid=1&nav=0,1
