Felenasoft

I have just started using Xeoma and I am also a relative newbie with Linux, and I am using ubuntu 18.04 lts

I have created a path for the files in ubuntu: which is Home/CCTV/xeoma
I've also changed the relevant permissions.

As I want to store the video files on my NAS server, I have mounted the path to my NAS server in the /etc/fstab file:
IP address of server:/mnt/CCTV/xeoma /mnt/CCTV/xeoma

In 'other locations' of the files manager, nautilus, there are folders for the NAS server IP address, and also the sub folders where video archiving was sent to for the 2 Hikvision cameras, which is strange as the 2 Merrit Liiln cameras sent the recording to my NAS server.

In the Preview and Archive, I have for the Folder or network path as: //ip address of server:/mnt/CCTC/xeoma

Hello and welcome aboard!
For Preview and Archive you want to indicate the directory, where the NAS was mounted. If the mounting was done correctly, in your case, it should be /mnt/CCTV/xeoma.
Additionally, you may want to unlock full access to that directory (chmod 777). You can test your mounting by creating, editing and deleting files in that specific directory. If you have access to all of the above - so should Xeoma.