cciefun ccie/sp fortiOS linux tcl/tk avalanche/reflector canada immi, visit

Vi tutorial

a, how to show line number in vim?
:set number <==> :set nonumber

b, how to open 2 windows:
:split xxx.txt or :vsplit yyy.txt
u can control the size of the new window: :3 split xxx.txt
ctrl-w to switch the active window.

c, where am I?
ctrl-g

d, search the string three?
/three
how to highlight the result?
:set hlsearch
:nohlsearch