Certificate for specific services:
0. Root CA
1. SIP services/Lync Front-end.
2. AV services/Edge .
1. SIP services. :
STEP 1. Goto run in windows button in lower left corner and type mmc.
STEP 2. In mmc window selecte File-->Add/Remove snap-in.
STEP 3. Select Certificates from Add/Remove snap-in.
STEP 4. Select Computer Account from Certificate Snap-in.
STEP 6. Select Personal->certificates from mmc console.
STEP 7. After that select the certificate you need to export and click right button of mouse and from All Tasks select export.
STEP 8. Just follow necessary stuff and get your certificate by instruction from next click.
For Edge server certificate follow the same process used in lync server certificate.
If you find it more complex please use Digicert utility.