If you have never done any of this before, then there is no way we can teach you in a single post. Even reading through manuals will be difficult as you will not find step-by-step instructions.
Ask your Veritas reseller for assistance - they should have qualified staff to help (probably for a fee) to get you started.
You can also book yourself on classroom or virtual classroom training or make use of free Veritas eLibrary training.
Start here: https://www.veritas.com/education-services
Links to manuals in Handy NBU Links in my signature.
As @Marianne said, you really need make a trainig on classroom or virtual, it does not matter, because you cant learn how netbackup works and administer it only with some posts...For now take a look this video, maybe it can help you to create and understand the process to create a NBU policy, there are others videos too assist you..
As soon as possible, make a trainig.
It is probably possible to configure a simple type of backup , for example policy type of 'standard' for Unix/ Linux backups, or MS-Windows type , for, well, Windows.
You need to configure a storage unit, this can be done in the NBU Java GUI, and will consist of tape drives, or disk storage (Basic Disk or Advanced). Anything other than this (MSDP, DataDomain, Cloud etc ... ) gets way more complex if you are not familiar.
Provding you have a storage unit, you need to create a policy, in here you specify the storage to use, create a schedule (Full or incremental + plus a window to tell the backup when to run), add the client(s) to backup and then specify the filelist (what to backup).
That s NBU at it's most simple - but, consideration has to be given as to what you will do in the future, what clients you group into each policy and manuy onlther considerations. In other words, the backup environment needs proper design before you touch the keyboard. Badly designed systems cause very major issues in the future and there are times that we just cannot fix them (under resourced hardware, too many jobs, live system so not allowed to make any changes etc ...).
Even installing NBU needs design - if Unix, it should be on it's own filesystem, ideally, with log areas, and image catalog on a seperate filesystem as well ideally. If windows, it shouldn't be on the OS drive (C:\), and seperate 'filesystems' are a good idea as per unix. Free space needs to be calculated to allow for growth of the system over the next 2 or 3 years.