If you cannot afford to go on a 5-day NetBackup training course or get a consultant to assist with installation, I suggest that you spend some time reading NBU manuals first.
You will need the Getting Started Guide, Installation Guide, Device Configuration Guide, NetBackup Admin Guide I and II as well as the Troubleshooting Guide.
All the manuals can be found here: http://seer.entsupport.symantec.com/docs/290282.htm
I do not suggest that you read all the manuals before getting started, but start with the manuals in the order that I listed them and read up till you understand the NetBackup architecture and what/how to install and configure. Keep all the manuals handy for reference if there's anything that you don't understand during configuration.
Good luck!!