Australia has a wide range of climates from the wet tropics to cool temperate climates and it is important to consider your climate when selecting trees that will be best suited to your area so they will thrive and be productive once planted. This map from the Organic Gardener Magazine is an excellent example of a climate map that will help you to understand what type of climate you live in.
If you are new to gardening it is a good idea to start with something that is ideally suited to your climate so that it will flourish and your success with one thing will inspire you to grow more and garden more. Understanding your climate is just the beginning as every garden will also have its own microclimate. Consider the aspect of your land, does it face north, south, east or west and where the sun is at it hottest. Where are your shady, cool damp spots and do you have a cold frost gully where the cool air pools on cold winter nights. Do you have a sheltered sun trap, do you have bare north facing walls that can be used to reflect the heat back onto heat loving plants during the winter. Understanding the lay of the land will be essential in helping you select the ideal positions for you favourite trees.