The OpsCenter Agent would be installed on the servers that you plan to collect data from, such as the NetBackup master server, or an Enterprise Vault server. For NetBackup, you only need to install this on the master server, not the media servers or clients. And I don't believe you need the Agent at all if you are using NBU 7.x.
The OpsCenter Server would be the server that will host the OpsCenter application. It will collect data from the OpsCenter Agents installed on the other server(s).
The View Builder is a separate app that would be installed on the OpsCenter Server. It is used to create groupings/lists of servers (called views), which can be used in the OpsCenter reporting to make it easier to create reports on specific servers. For instace, we have a view defined that we can use to narrow the reports to just our SQL backups, another view to report on just the Oracle backups, etc. You can still create reports on individual servers, this just makes it easier to pre-define them so you don't have to scroll through hundreds of server names every time you want to create a report.
We have the OpsCenter Agent installed on our Solaris NetBackup master, the OpsCenter Server and View Builder are installed on a windows VM.
