SSH connections is only required (later) for adding a CMTS-Tunnel OR if you want to make deeper changes towards NMS Prime instance .
If you want to login via SSH please unzip the nmsprime.zip which you got through email after creating your NMS Prime cloud instance.
Then open a terminal in the folder where you extracted the zip and run the following commands:
SSH login
ssh -i your-key-file centos@your-nmsprime-vm-address
Make sure to input the name of your-key-file (which has the format like key-for-nmsprime_YYYmmddHHiiss) and also insert your-nmsprime-vm-address (which has the format like abcdefgh.vm.nmsprime.com).