Rails API: make application controller serve JSON

This tutorial from Fancy Pixel says:

Now we need to change the application controller so that it inherits from ActionController::API, and kiss the protect_from_forgery goodbye. Since we are serving only JSON, it makes sense to add

respond_to :json

to the applciation controller, helps DRYing all out. While we are at it, we might as well delete the assets and views folders, we won’t need them.

I am not sure about what I am supposed to do.

This is what my application controller looks like:

class ApplicationController < ActionController::API
    respond_to :json
end

Is it correct?

Also, should I keep or remove protect_from_forgery with: :null_session :

class ApplicationController < ActionController::API
  protect_from_forgery with: :null_session
  respond_to :json
end