What is command line? Command line is black window, command line is blue window, command line is ??? Whatever you say… I just want to say that command line is just like what you have done until now. Click here, click there, opening your favourite software, copy file and then paste it. Really… Indirectly, you have done your command line. Then, you will ask “… Then, where is the black window or something black that you have mentioned in above?” Okay, what you have been done in here is what it had been called GUI, stands for Graphical User Interface. And for command line, it had been called TUI, stands for Text User Ineterface. Both of them still used until now. GUI and TUI have it own plus minus point, for example, if your computer suddenly slower than before (it could be your RAM is unsufficient), you can use TUI to run your program. TUI just need small amount of RAM. The using of TUI need the user to study it first… What word to be typed and so on. Too mamy rules that you must obey it or if you do not obey it… it won’t work. There will be error message appear in your monitor. But don’t worry, it won’t damage your system. GUI is simple, Just need any pointer like mouse or other then point to something in desktop and it will be running just like you type in TUI. But, i takes too much RAM.