As the name implies, this visa allows Australian citizens, Australian permanent residents, and Eligible citizens of New Zealand to come and live permanently in Australia as married partners (i.e., opposite-sex spouses) and de facto partners (i.e., those in a same-sex relationship).
The partner visa may be largely classified into two categories: prospective marriage visa and partner visa, although having three main subclasses. The kind of relationship you are in will determine what kind of visa you need to apply for.
Intended marriage (Fiancé): Prospective Marriage visa
Married relationship (Spouse): Partner visa
De facto partner relationship: (including a same-sex relationship): Partner visa
Both temporary and permanent subclasses exist. Partners who first fulfill the legal requirements for a visa are given a temporary visa. If there is a long-term partnership or children from the relationship, a permanent visa may be issued shortly after the temporary visa is granted, or after an eligibility period. Additionally, fiance(e)s—intended spouses—of Australian citizens, permanent residents, and qualifying nationals of New Zealand are permitted temporary entrance into Australia under the partner category migration.
It should be noted that being the spouse or fiancé of an Australian citizen, permanent resident of Australia, or eligible citizen of New Zealand does not provide you automatic residency rights in Australia. Applying for a permanent visa and having it evaluated against the legislative requirements is the first step towards becoming a permanent resident of Australia.