Hi amitkj,
host entries are only required when name resolution using DNS is not working properly. A Data Protector client needs to find the Cell Manager using its hostname and vice versa. I'm not able to tell you what the backup specs do. Adhoc usually means that they are executed on demand by an administrator or operator. They are specific to your environment and you might need to ask the one who configured it or look through the configured settings. F1 help is pretty hand to explain all the available options. If you're that new you should check the available documentation in the Omniback\Docs folder.
Regards,
Sebastian Koehler
