the" commonwealth of australia" consist of the australian mainland, the island of tasmania, and numerous smaller islands. it is a very large country. the population in only 25.6 mio though. the capital city in canberra, while the two largest cities are melbourne and sydney, both more than 4 mio residents. the landscapes vary immensely - deserts, tropical rainforests, agricultural areas, and high mountains.
mini-history: australia has been settled for at least 50 thousand years. these people, called aboriginals, were technologically far behind and could not write. they created impressive art though.
they never organized them as some kind of federation. when the european settlers came, they could not uphold their land ownership, and became just kind-of prey. the immigration started 1788, when the "first fleet" arrived, sent by the british government. the intention was to establish a new penal colony. and this happened, around sydney and near hobart in tasmania. then step by step colonies were set up, for settlers from great britain, but eventually other european countries as well.
australia strived increasingly for independence. in 1901, the "federation of the colonies" was formed, and in 1907 it became officially a "dominion". melbourne was the temporary seat of government from 1901 to 1927 while canberra was being constructed. the "head of state" is still the british queen or king, because australia is not willing to have an own president.
personal note: i live in melbourne since 1994 - so the reported tours in australia are spread out over a time frame of 25 years.