Authorization with cancan

After looking at the ability.rb. I have allowed the admins to manage
everything (that part works) but how do I allow the user to just, view
and edit their own Logg using cancan? At the moment the users cannot
view anything at all, not even their own created logg. But admins can do
everything.

class Logg < ActiveRecord::Base
has_and_belongs_to_many :user
end

  class User < ActiveRecord::Base
    devise :database_authenticatable, :registerable,
     :recoverable, :rememberable, :trackable, :validatable
      ROLES = %w[admin moderator author banned]
   has_and_belongs_to_many :logg

end

I have no User controller. I have the loggs controller:

class LoggsController < ApplicationController

 before_action :set_logg, only: [:show, :edit, :update, :destroy]
 load_and_authorize_resource

  respond_to :html

 def index
 @loggs = Logg.all
respond_with(@loggs)
 end

def show
respond_with(@logg)
end

 def new
@logg = Logg.new
respond_with(@logg)
 end

def edit

end

 def create
@logg = Logg.new(logg_params)
@logg.save
respond_with(@logg)
 end

 def update
@logg.update(logg_params)
respond_with(@logg)
end

def destroy
 @logg.destroy
respond_with(@logg)
end

 private
 def set_logg
   @logg = Logg.find(params[:id])
 end

 def logg_params
  params.require(:logg).permit(:name, :date, :time,

:whats_gone_well_this_week, :whats_not_gone_well_this_week,
:learnt_anything_new, :what_would_you_like_to_improve, :anything_else)
end
end

class Ability
include CanCan::Ability
def initialize(user)

   if user.nil?
  cannot :read, Logg
  elsif user.admin?
  can :manage, Logg
 else
  can :create, Logg, :user_id => user.id
  can :update, Logg, :user_id => user.id
  end
  end
end