Where to write the shell script?
 

I would like to know where to write the shell script? What tools to be use? use Gmac?

If you want to write them in the terminal, you can use vi (which is a bit difficult at first) or nano (which is quite similar to the DOS editor). But you can also use Kate, KEdit, KWrite or Emacs or another text editor of your choice.

i am using redhat 9, i remember long time ago (i am using redhat 8), there is an editor quite similar to dos editor....is that call Nano? i am not sure about it. ...but i cannot find these things from the program.

Redhat uses Gnome by default. The default text editor is gedit.
In your GUI menu, there should be an entry for "Text Editor".

You can of course install any editor you want.