scaffold return to index page

i am using rubyonrails 2.1 and i have used scaffold .on controller i
added new method and html.erb now what i want is to back to the
index.html.erb page of the scaffold ,i have tried to use render but on
the original scaffold i have met the problem on the below
"You have a nil object when you didn't expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.each"
can any one tell me what should i do thanks.

you must use redirect_to, render :action only display the action it
does not execute the method