After serval difficult expriments, now i porbably have a knowledge of some basic orders.Meanwhile, i have some other common sense about it.Aside from the easiest order 'who' to look who is online, i have tried some other orders. When we entry 'time'， it can calculate the time that a program runs. If we don't have a program running, what shows on the screen is 'real 0m0.000s? user 0m0.000s? sys 0m0.000s'. It's so amazing. It is worth paying attention to 'kill' order. It can be written to kill a program. We can enter 'Ctrl+C' to end a downstage program, however, we can only use 'kill' order to kill a Background program. So it is useful to end a program when it needs to be shutdown forcely. Athother order that i am familiar with is 'cd' order. When it is entryed, such as 'cd work/', it can jump to the work list. Next week, i will learn the System across-the-aboard and more skills to operate the system more proficiently.