Authentication->Simple Login Form..(chek user if you r there or not)
Authorization->Role Base System(Check you are admin or client.if you are admin you can assess data which u r allocated to use... and ....if u r user.you can access only ur page ..which permission given By admin:)
Please refer to the following link to know the differences between authentication and authorization,
http://onlydifferencefaqs.blogspot.in/2012/08/difference-between-authentication-and.html
Authentication is a process of verify the user and Authorization of process of verifying whether the authorised user is allowed to access the resource or not.