# Using Linux

i have some queries..i was trying to find out some commands in the manual..
like,,

--what command can be used for compressing files in Linux..

--how to check man page for /etc/passwd ?

--and i am not clear with this uid command?
why is the "set uid bit" set for "su" command?

--and in killing processes,why does killall -e doesn't work??

And please tell about interesting and hard to figure commands which you are familiar with..