I bought one of these and now I’m unclear what I should be doing regarding RAID. Can I not add drives later?

I’m not sure if I’m looking at old data but I’m starting to feel stupid. I’m not super tech literate but I’m typically above average. Also a lot of doom and gloom telling me redundancy isn’t a backup like I don’t already know.

It’s still in box and considering returning it.

Any advice? Sorry for the vague question.