So here is the process for my Exchange 2013 lab certificate creation.
Select servers, certificates.
Select the plus sign to create a new certificate.
Now to the CA
Select the “Advanced Certificate Request” option
Now Select the “Submit a certificate request by using a base 64………….”
Copy and paste the request into the box.
Select “download certificate”, then select “Save”
Save and copy to Exchange server (where you saved the pending request)
Complete pending request
Assign to services
Now go play some more with your new Exchange 2013 LAB.