TS251 and Single HDD

Hello… i have upgraded my existing hard drive to a 6tb WD Red Pro
I have a TS251 and have only ever used 1 of the 2 bays for my Movies / Shows etc
I have everything backed up to an old HDD that i never use so i dont worry if i loose any data as i have copies.
Im trying to set up this new HDD but following videos etc im having a problem in creating the maximum space available…
I get lost on a lot of the youtube videos, it may be my 65 years of age but i dont seem to be getting the maximum storage
I create the initial volume for the system files and then the Storage pool… i then create another storage pool and try to have it set to the 5 tb of space thats left but its only creating a pool of like 200 gig ???
Can someone tell it to me in a very simple way like im a 5 year old please …

You can only create one storage pool per disk…something is not right there

OK thankyou…
I cant find a video that just shows a single hard drive set up… THanks for that

So to start with the 6tb drive… what size Volume would be a good start, its wanting to make the volume 1.2tb… is that a bit excessive ?

and that will only give me 3.97TB of storage space for all my data to go on … im like losing 1.5tb

You can do two things,

A static volume: All the space is reserved for storage (easy for beginners)
A pool with tick or/and thin volumes: More flexible but harder to wrap your head around for beginners)

If you just want to store files on the NAS, just go with a static volume and be done with it.