map.connect ":name", :controller => "app" where name is a GET parameter feed into the url on a link_to (or you can type your domain_name/<whatever_name> to access the page directly).
Ff I'm reading it correctly, you want to get to the action 'abc' with a controller of 'app'?
map.connect "abc", :controller => "app", :action => "abc"
This only requires the controller and the action when you create a link_to. As for the url, "domain_name/abc" should work.