When I got a separate device such as a hard disk bought recently, I used the mount command to make the files on the device visible. I could also add files. The commands were available for the superuser.
mount -t ext3 /dev/sda1 /home/nameOfTheUser/folder/disk/folderA
-t ext3 meant the file system called ext3.
/dev/sda1 was the name of the device.
/home/nameOfTheUser/folder/disk/folderA was the folder I used to view my files.
Automatic use every time
I added the line below:
UUID=1gfdjfj3-gcbn-378d-127c-3shfjhrwyrgc /home/nameOfTheUser/folder/disk/folderA ext3 defaults 0 0
I saved the file.
I read the pages on UUID. I also read a page on mounting partitions and another page on the same topic. A page gave many examples.