Ruby on Rails beginner: Unitialized constant SessionsHelper::User

I am just starting out learning Ruby on Rails and am trying to design a microposts site where users can post and follow other users. I keep getting this error "uninitialized constant SessionsHelper::User. I have set up the controller SessionsHelper.rb as follows and am not sure why I am getting this error - do I have to initialize "user" some other way or somewhere else?

SessionsHelper.rb file:

class UsersController < ApplicationController
  before_filter :signed_in_user,
            only: [:index, :edit, :update, :destroy, :following, :followers]
before_filter :correct_user,   only: [:edit, :update]
before_filter :admin_user,     only: :destroy

def index
 @users = User.paginate(page: params[:page])
end

def show
  @user = User.find(params[:id])
  @microposts = @user.microposts.paginate(page: params[:page])
end

def new
  @user = User.new
end

def create
  @user = User.new(params[:user])
  if @user.save
    sign_in @user
    flash[:success] = "Welcome to the Sample App!"
    redirect_to @user
  else
    render 'new'
  end
end

def edit
end

def update
if @user.update_attributes(params[:user])
  sign_in @user
  flash[:success] = "Profile updated"
  redirect_to @user
else
  render 'edit'
end
end

def destroy
User.find(params[:id]).destroy
flash[:success] = "User destroyed"
redirect_to users_path
end

def following
@title = "Following"
@user = User.find(params[:id])
@users = @user.followed_users.paginate(page: params[:page])
render 'show_follow'
end

def followers
@title = "Followers"
@user = User.find(params[:id])
@users = @user.followers.paginate(page: params[:page])
render 'show_follow'
end

private

  def correct_user
  @user = User.find(params[:id])
  redirect_to root_path unless current_user?(@user)
  end

  def admin_user
    redirect_to root_path unless current_user.admin?
  end
end