I am going to add following line to the /etc/fstab file

/dev/sda4 /MyApp ext3 noatime,errors=remount-ro 0 5

Does it also create directory "MyApp"? Or which kernel file is responsible for creating the directories?

Also on linux, which kernel file is able to create some soft links and additional directories?

Thanks in advance.

Have not tried putting entries into /etc/fstab that are not existing directories. You could try it and boot up to see if it creates the directory on your system!

The kernel is not responsible to create that directory, nor is the mount command. /etc/fstab is a static configuration. It does not think, it does not check, it does nothing except printing a small error if your line have a problem. If you want the directory to be created and additional control over the whole mount process, then use /etc/udev/rules.d/ instead of /etc/fatab. You can also use the preconfigured "udisk" config for udev. When you plug an USB thumb drive and a folder is created, it is done by udev or HAL (deprecated) for some older distributions.

You must create the mount point if it does not exist.

I have tried mounting to a not-existing-directory and can testify that it does not work.
You may have noticed the existing mount points at /mnt /mnt/tmp, etc., etc..
Some like all that organization, but that is too much typing for using them at a console.
I create custom mount points under the root directory for every partition, drive and usb port,
such as /d1 /d2 /d3 /s10 /s11 /s12/ /usb1 /usb2, etc..
Then have your fstab use those mount points.
Then you can
>> mount /s10
and it gets the rest from the fstab line for /s10.

KDE also has a mount tool.
Unless KDE has fixed this in the latest releases, do not mount using the KDE system tool, because it will not let go when you try to un-mount.
I always bring up a console and use a mount command, and for that reason I install the console device on the X-windows taskbar so it is handy.

To create a soft link
>> ln -s existing-dir link-name
see: man ln

To create a directory
>> mkdir newdirname
see: man mkdir

When you cannot find a command, such as linkthis for example, then search the man pages by doing
man -k linkthis

Some commands are part of bash, so to find them you must:
man bash
info bash

This also can be done in KDE, but I never do it that way, and they
keep changing things, so I do not know where to look in the menus.