If you want to learn to fly, there are plenty of options.  You might want to fly for a hobby, or you might want to make aviation your career and sit up front of a Boeing 787 or an Airbus A380.  Whatever your reason, you'll need to progress through a range of licence levels to get where you want to go.

The various steps are as listed below:

• Trial Instructional Flight (TIF) - A short flight with a qualified instructor to see if it's really what you wnat to do.
• Student Pilots Licence (SPL) - You'll need this to start your proper training.
• Recreational Aviation (RA-Aus) - A licence that allows you to fly smaller RAA registered aircraft (eg, Light Sports Aircraft, Ultralights) within a restricted area.
• General Flying Proficiency Test (GFPT) - The basic licence that allows you to carry passengers in a restricted area - but not for money.  (This used to be called the RPPL - Restricted Private Pilots Licence).
• Private Pilots Licence (PPL) - The licence that gives you the freedom to fly anywhere in Australia, carrying passengers, in an aircraft for which you have gained endorsement. But still - not for money.
• Night Rating (Night VMC) - An endorsement that allows you to fly after dark.
• Instrument Rating (IFR) - An endorsement that allows you to fly in all weather conditions
• Commercial Pilots Licence (CPL) - The minimum licence you will need if you want to work as a pilot and get paid for it.  Examples include Air Charter, Agricultural (crop-dusting), Flying Instructor. 
• Airline Transport Pilots Licence (ATPL) - The top level - you'll need this if you want a job with one of the major airlines and have plans to fly the big passenger jets.

The pages linked above give some basic information about each of these licence and endorsement levels, and provide links to more detailed information from CASA.