These handy links provide information for registering and using trailers from relevant authorities in each state.
Trailer registration information - https://www.qld.gov.au/transport/registration/register/caravan
Towing safety road rules and tips - https://www.tmr.qld.gov.au/Safety/Vehicle-standards-and-modifications/Loads-and-towing/Safe-towing.aspx
Trailer registration information - http://www.rms.nsw.gov.au/roads/registration/index.html
Towing safety road rules and tips - http://www.rms.nsw.gov.au/roads/safety-rules/road-rules/towing.html
Trailer registration information - https://www.vicroads.vic.gov.au/registration/new-registration/register-a-trailer-or-caravan
Towing and vehicle safety tips - https://www.vicroads.vic.gov.au/safety-and-road-rules/vehicle-safety
Trailer registration, trailer standards and towing information - https://www.sa.gov.au/topics/driving-and-transport/vehicles-and-registration/vehicle-registration/vehicle-types-and-specifications/light-trailers-and-caravans
Trailer registration information - http://www.transport.wa.gov.au/licensing/license-a-trailer.asp
Boat trailer information - http://www.transport.wa.gov.au/imarine/trailers.asp
Trailer registration information - https://www.nt.gov.au/driving
Driving safety information - https://www.nt.gov.au/driving/safety
Trailer registration information - http://www.transport.tas.gov.au/online/vehicles
Trailer requirements and specifications - http://www.transport.tas.gov.au/vehicles/specifications/light-trailers