The Partner migration is divided in two categories prospective marriage visa and Partner visa.

Prospective marriage visas are given to people that are engaged to an Australian permanent resident or Australian citizen, and whom  they have met face to face before the application.

The applicant must be overseas  and the application can be only lodged overseas as well.  

A prospective marriage  visa is given for 9 months so the applicant and her/his fiancé can get married within that time and then apply for a partner visa in Australia.

Partner visa is for people that are in a marital relationship,  in a De facto relation ship for 12 months (or more) or in a De facto registered relationship. 

The visa application can be done in Australia or overseas depending of the location of the applicant.

This visa is given in two parts temporary residency followed by a permanent residency (after providing relevant evidence and eligibility period).