I need a Finnish language expert to help me with this please!!?

Hello. I am learning this very difficult but interesting language of yours but there is some stuff i don't understand. In finnish you have endings that define the relation between the word and a person or an object. For ex. : H�nen talonsa (nsa) Teid�n talonne and so on. There is some endings i don't understand like : Parhaimmillaan (aan) "aan" refers also to he/she or it but it is not "nsa" like in talo. Can someone please tell me why it differs, is there a grammatic rule for this? and would you give some good examples? thank you!