Australia receives so little rainfall that about 35% of Australia is classified as a desert.
70% of the country is classified as arid or semi-arid, which means it gets less than 500 mm of rain a year.
That makes Australia the driest inhabited continent on Earth. Only Antarctica is drier.
Only 3% of the Australian population live in the “dry” 70% of the continent, the rest of our population is concentrated on the coast.
Like most major deserts across the world the Australian deserts can be found around a certain latitude (roughly 30° north/south of the equator) where the weather phenomena create a dry climate.
Hot moist air rises at the equator. It cools as it moves north or south, the moisture condenses and falls as abundant rain onto the tropical regions.
Finally the now dry air sinks over the subtropical regions, warming as it sinks, which encourages evaporation, and voila: you get more evaporation than rain, perfect conditions for the formation of a desert.