Rails 3 helper methods not available in controllers even after explicitly including them -

fist of i'm newbie rails.
have in sessionscontroller:

def method   sign_in 'user' end 

and in sessionshelper:

def sing_in(user)     ...... end 

so googling , reading answers on stackoverflow let me try this:
including 'sessionshelper' sessionscontroller , tried put in 'applicationcontroller' this:

class applicationcontroller < actioncontroller::base    protect_from_forgery   include sessionshelper    def handle_unverified_requests     sign_out     super   end end 

but i'm getting

nomethoderror : undefined method `sign_in' sessionscontroller:0x007eff2004fcd8

also few questions:
1) what's point/difference in putting few methods in heplers , few in controllers? security issue or what?
2) tried puting sign_in method in sessionscontroller read in stackoverflow methods defined in controllers can accessed in views. avoid problems in views used

helper_method

but still same nomethoderror
3) best , easy way access helper methods in controllers?

so going wrong.
i'm using rails 3.2.11 , ruby 2.0.0p0

looks typo: helper method 'sing_in' instead of 'sign_in'.