Want write a script

Hello,
Dear friend,

I want write a script which will copy the containt of one Text file to another Text file automaticlly.Means if i make one file on my /home & create a copy(not shortcut) of it on desktop. Now i want, if i modify a file of desktop, so file in /home should be modified automatically.
I don't know how to write script.but i want learn & want become Master.

Thank You,
Vishesh Joshi