Not sure how much you know about NASs, so forgive me if there’s too much info here. I’m also not a huge techie, and may be working off old info. But here goes:
The NAS is not a normal drive at all. Because it needs to work unattached to a PC/Mac, it’s a small computer running Linux dedicated to storing and serving files. So in the main you need to use the applications that come on in.
To get files on/off the NAS, you can see the drive on your network devices, and use your laptop/PC to copy. But this copying process involves the transfer going via your computer and it’s RAM, and it’s a bottleneck for moving large files around. If you have a USB drive attached to your laptop with your music on for example, you’ll need to copy this to your NAS via your laptop.
So to get round this, the OS on the NAS typically comes with a suite of tools to help with all this file activity, that you can access remotely via a web browsers. And this should include some back up/in take stuff. In my experience, the Synology has the better suite of tools (although the UI won’t win any awards).
What I would look for is a NAS that has the ability to add an external HD via USB (a fast USB connection), and the NAS software offers the means to read/write/backup to that drive. My original rubbish WD product didn’t offer that.
The other - obvious thing - to point out is that the NAS rapidly becomes the largest storage device you have, so you will need an equivalent sized drive to back-up…
I’m happy to be corrected by more knowledgeable people on the forum…