By choosing an option logout through the session indicator on the far right side of the top panel.

(i) Ubuntu has less hardware support for commercial/industrial/medical/ logistical therefore its less voted for use in big time backends.
(ii) Ubuntu doesn't support middlewares such as C panel, cloud linux and a plethora of other infrastructure or monitoring tools.
(iii) Hard to install graphic drivers especially for old hardwares. It is not possible to play the modern games, because of poor graphics quality.
(iv) The user switching from windows will not like the user experience on Ubuntu and will have difficulty in operating the OS.
(v) Ubuntu is not capable of playing MP3 files by default.

Yes, hard drives and floppy drives are represented with drive letters.
A: drive is used for floppy disk of 3.5 inches and storage capacity of 1.44 MB.
B: drive is for floppy of size 5.25 inches and of storage capacity of 1.2 MB
So, we can say like
A: First Floppy Drive
B: Second Floppy Drive
C: D:E:.....Z: Hard Disk Drives, CD/DVD

In Ubuntu OS:
(i) Create a file: By right clicking in the desktop and also files be created by using file menu.
(ii) Delete a file: By using right-click choosing a move to trash or by using the menu.
(iii) Rename a file: By using right-click and choosing rename option.
(iv) Save a file: Press ctrl + x or F2 to exit. You will. then be asked if you want to save. (or) Press ctrl+ 0 or F3 and ctrl + x or F2 for save and exit.
In Windows OS:
(i) Create file: Open an application and create by using file menu.
(ii) Delete a file: By right click on a file and choosing the delete option to delete a file.
(iii) Rename a file: By right click on a file and choosing rename option to rename a file.
(iv) Save file: Press ctrl+S or file - save to save the file.

Elements of Ubuntu:
Search your Computer Icon:
This icon is equal to search button in Windows OS. Here, you have to give the name of the File or Folder for searching them.
Files:
This icon is equivalent to My Computer icon. From here, you can directly go to Desktop, Documents and so on.
Firefox Web Browser:
By clicking this icon, you can directly browse the internet. This is equivalent to clicking the Web Browser in Task bar in Windows.
LibreOffice Writer:
This icon will directly take you to document preparation application like MS Word in Windows,
Libre Office Cale:
This icon will open LibreOffice Cale application. It is similar to MS Excel in Windows.
LibreOffice Impress:
By clicking this icon, you can open LibreOffice Impress to prepare any presentations in Ubuntu like MS PowerPoint.
Ubuntu Software Icon:
This icon will let you add any additional applications you want. This can be done by clicking the Update option at the top right corner of that screen.
Online Shopping icon:
Using this icon user can buy and sell any products online.
System Settings Icons:
This icon is similar to the Control panel in the Windows Operating System. But here, you need to authenticate the changes by giving your password. You cannot simply change as you do in Windows.
Trash:
This icon is the equivalent of Recycle bin of windows OS. All the deleted Files and Folders are moved here.