How high is the temperature in Australia in winter? Do you need to wear cotton-padded clothes?

Winter in Australia is in June. Because Australia and China span nearly a quarter of the latitude of the earth, its northern part has a tropical climate, and its southern apex has a sub-frigid climate, so your question is too extensive to answer.

For example, I am in Sydney now, and the coldest night in winter is about 6- 10 degrees. I'm a boy, so a sweater and a coat is enough when I go out. Girls may wear more clothes. It doesn't snow in normal winter in Sydney.

For example, Melbourne is much farther south than Sydney, and the average temperature is about 4 degrees lower.