form_for for a has_one relation model

I’m new in rails and I have the following question:

I have two model

user and user_informacion:

class User < ActiveRecord::Base attr_accessible :email, :password, :password_confirmation has_one :user_information has_secure_password before_save { |user| user.email = email.downcase } before_save :create_remember_token VALID_EMAIL_REGEX = /\A[\w+\.]@[a-z\d\.]\.[a-z]+\z/i validates :email, presence: true, format: { with: VALID_EMAIL_REGEX }, uniqueness: { case_sensitive: false } validates :password, presence: true, length: { minimum: 6 }, confirmation: true, unless: Proc.new { |a| !a.new_record? && a.password.present? }

def send_password_reset
      self.password_reset_token = SecureRandom.urlsafe_base64
      self.password_reset_at = Time.zone.now
      self.password = self.password
      self.save!(:validate => false )
      UserMailer.password_reset(self).deliver
  end

def reset_password_token
    self.password_reset_token = nil
    self.password_reset_at = nil
    save!
end

private

def create_remember_token
    if self.new_record?
        self.remember_token = SecureRandom.urlsafe_base64
    end
end

end

class UserInformation < ActiveRecord::Base belongs_to :user attr_accessible :address, :address2, :business, :descripcion, :identification_number, :mobile_cell, :name, :phone_number validates :address, presence: true, length: { :maximum => 250 } validates :address2, length: { :maximum => 250 } validates :descripcion, presence: true, length: { :maximum => 300 } validates :identification_number, presence: true validates :phone_number, presence: true, length: { :is => 11 } validates :mobile_cell, :length => { :is => 11 } validates :user_id, presence: true
end
As you can see User has_one UserInformation

My routes are like this:

resources :users do member do resource :user_information end end resources :sessions, only: [:new, :create, :destroy] resources :password_resets

root to: 'users#new'

match '/signup',  to: 'users#new'
match '/signin',  to: 'sessions#new'
match '/signout', to: 'sessions#destroy', via: :delete
I having a lot of problem tying to figure out how to make a form_for for my create action of my user_information. I tried with form_form(@user_information) do |f|, form_for([user, user.user_information.build]) do |f| but I always get an error. Does anyone can help me with this form_fom, please??? The form_for if for my new view of may user_information.