How to pass search parameter to ruby from index file

I have a search box in my html file
I want to pass the search string from this html file to the search
controller. My rhtml file has the following to do the search and it

<%= start_form_tag :controller => ‘rents101’, :action => ‘searchads’ %>

<%= submit_tag “Search” %><%= end_form_tag %>

I tried using the text field with name “typed_search” and post action to
“/rents101/searchads” and it did not work

any ideas?
thanks for your help