The Dreamtime is the period in which life was created according to Aboriginal culture. Dreaming is the word used to explain how life came to be; it is the stories and beliefs behind creation. It is called different names in different Aboriginal languages, such as: Ngarranggarni, Tjukula Jukurrpa. In the Dreamtime, the natural world—animals, trees, plants, hills, rocks, waterholes, rivers—were created by spiritual beings/ancestors. The stories of their creation are the basis of Aboriginal lore and culture. And are also what are often painted by Aboriginal artists.
In the lore, all living things were either the ancestors themselves, or were made by the ancestors. That is, a river may be an ancestor and may also be a creation snake.
The Dreaming explains how things came to be – why a rock is in a certain place or a particular shape, why the echidna has spikes, why the moon returns full every month, how kangaroos got their tails. 
The Dreaming also commands the rules and ways of being in Aboriginal culture. Dreaming stories explain these beliefs, such as: the lesson not to hurt animals; who one should marry and bear children with (according to the Aboriginal skin system), who one should not talk to (according to the Aboriginal skin system), how one should show respect in another's Country, how one should welcome strangers to your own Country. It dictates how one should behave in certain circumstances. These stories are the cultural rules and obligations Aboriginal people are expected to live by, within their culture.
The Dreaming is not static or linear. It is the past, but it is also the present and the future. The Dreaming it is constantly evolving to explain events and changes today, such as floods, storms and (negative and positive) occurrences in people's lives.