[ns] please help

[golrokh m]

i'm a beginner to ns2. 
I installed the NS2.34  on obuntu. and it's validated. now I'm going to start 
with a simple example that I found from the net.i save it in my home folder.
 when I write $ns simple.tcl
 it says:
simple.tcl does not exist, try again
I know that this error is for directory, but how i can fix it? i mean  1) at 
first where I should save the simple.tcl file ? 2) which directory i should 
use?would you please write the exact directory? 
thanks so much if you help me .