Hi.
This is written with one of those online translators, sorry for the mistakes.
Let’s see. Using a modern desktop is not the same as it was just a few years ago, and sometimes we start with the superficial part instead of going to the basics. In fact, this thread is called “how to modify /etc/fstab”. One answer to this would be how to use vim, how to use sudo and the basic structure of an fstab file. Another way to do it might be to launch dolphin as root and open the fstab file normally (you would still need to know something about fstab).
This is different from the general question of how to add a disk. Windows has been using each device as a separate drive for a thousand years and people get by. In fact, it is possible to mount any device in a folder, as we usually do here. And yes, on a modern desktop you can do something similar, although it asks you for the key because it assumes that the device is going to be mounted as read-only. I’d like to one day include the rules for ext4 that we include for FAT and even NTFS, but that day is not today.
In order to mount a disk or partition from dolphin without asking for the password, we need that folder to be owned by the user. What happens is that the temporary folder that is created can have a strange name and not very easy to handle from the command line for a beginner. A simple way to get around this is to use dolphin to open the command line right there. You will need to do this because dolphin running as a user cannot change permissions on files owned by root. To do this, you will need the command line as described above (sudo chown…).
Another way to do this is to use dolphin as root, which should be available in the applications menu → System. Or by running kdesu dolphin from a terminal. This lets you open fstab with kate too, for example.
This simply allows access to that device from dolphin and other applications that handle that kioslave. For best use you can make sure Plasma mounts that device on boot: System settings → Removable device → Removable devices.
A different option to all this, and it’s what you were trying to do, is to add a fixed mount point for the system. I don’t recommend anyone to modify fstab by hand right off the bat: it’s easy to make mistakes. Instead you have the wonderful YaST partitioner. You don’t need the mount point to exist: when you select “mount”, in the path you just type the name of the desired folder. If it is /home/guus/newThings, newThings should inherit the permissions from guus (check it). Also, when formatting the device it already asks you “what do you want it for”. If you don’t want to format it, go to edit device and click on “fstab options” and you’ll see something you should check.
Cheers!