Every new-commer always ask that question. If you came to Linux, it means that you like and want to know more about computers. Otherwise you would have stucked to Windows. You should feel good that you wanna know things. Don't feel bad, none of us were born with a manual, and all of us were (or still are) newbies.
If you used Windows before (98.4513% you probably did) you probably know about DOS. You can go to your start menu and under accessories(I think) you can open a DOS-prompt. A shell is basically an immesly enhanced version of the DOS-prompt. You can do alot more with a Linux prompt, "a shell", that you can do with a DOS-prompt. But, if point and click is so easy, why do you need a window to type commands?
Many programs available in linux don't have a visual version, you have have to execute them using the shell. That way, you can manipulate/view the outcome of the program. Imaging, if you have a program that searches and deletes files, but doesn't have a 'window', how do you know the actual outcome. In this case, you would log onto a shell, execute the command, and some output would be shown on the shell. It is possible not to use the shell, but you would be missing out on alot of little useful programs that don't have a visual version -- a version with a GUI(graphical user interface), for example.
if you ever decide to start learning programming, garantee you will start writing programs that don't have a GU. It's just alot easier to make those. Then, once you master your programming language, let's say C/C++, you might want to move onto creating applications with GUIs.
is it for multi users to connect at the same time to the system??
if though this means the benefit is to connect remotely ( telnet ,...)???
is this limited to 6 users only ( number of shells i can open ) ????
or 6 shells reflects the number of processes
Why can you have multiple shells?
So you can do multiple things at once. Maybe you're running a program in a shell and that program its taking over the shell while it's processing. You might then wanna log onto another shell so you can do something else. Think of it like having many windows open. This does not reflect the number of people that can telnet, or ssh into your machine.
Just think of a shell as a Linux (or more precisly Unix) version of a MS-DOS prompt.