rails action_controller usage

Question

I digg into some project with long development history

Maybe it's newbe question:

For specific controller I found thats it inherited from ActionController like so

class GraphController < ActionController
end

and seems it used for API cause when I add some actions there they shown without layout can anybody point me to some good article about ActionController usage. I check documentation but can't find any good explanation for tats stuff

Answer 1

http://guides.rubyonrails.org/action_controller_overview.html contains a good description of ActionController basics.