How to create a stgunit on Netbackup appliance

Well I don't think it is correct, you actually can create as many storage units as you want. What you can't do is to have more than one deduplication pool and more than one advanced disk pool per appliance. But on top of each of these pools you can create as many storage units as you want.

Oh yes. I think I got completely confused with Disk Pool. In fact I was thinking that the question is asked in that direction. 

Thanks for correcting me Mouse. ?? :)

But creating different storage unit is not going to solve any purpose. I cannot think of any.. May be number of backup streams, fragment size, thats it.. 

I can only think of one use of them, when you want to limit bandwidth usage for duplications, it is defined per stream in NBU so if you don't want to limit bandwidth for your normal backups, you can create a storage unit for duplications to use and allow minimal number of streams to be just in the defined limit.

@adivya1 is a person of few words....

We have no idea what current configuration looks like and what type of STU he/she wants to add.

Do you have a tape library attached to the appliance?
Or another type of STU?

Is this a real environment or theoretical (I noticed that you have tagged the post with 'Case Study')?