At first the Aborigines regarded the strange white men in large ships as ghosts, possibly ghosts of their own ancestors. They were prepared to deal with them peacefully. As long as the two groups of people stayed out of each other's way, there was no conflict.
The real problems started when cultural misunderstandings occurred. In one example, Captain Arthur Phillip sought to meet with an aboriginal tribesman on the beach. In standard English manner, he thrust out his hand in welcome, to shake hands. Not understanding the cultural context, the Aborigine believed it was an act of aggression, and speared him in the shoulder.
The Aborigines had no concept of ownership, and they did not see why the white strangers couldn't share the land. They also didn't see why they were not permitted to spear the big, easy-to-catch livestock of the white settlers for their own food. These beasts were valuable and so naturally, the white settlers saw the aboriginal actions as attacks, and hostilities began to grow, with landowners sometimes gathering together and setting out to eradicate groups of "troublesome" Aborigines.
In Tasmania, one of the earliest massacres of Aborigines occurred when the European settlers thought they were being attacked. All that really happened was that a party of around 300 aboriginal men were on a kangaroo hunt, and inadvertently stumbled across a white settlement. The "Battle of Risdon", as it came to be called, resulted in the deaths of anywhere between 3 and 50 Aborigines (eyewitness accounts vary dramatically), all because the Aborigines were hunting kangaroos. They had not formed an attacking party. This was the start of years of conflict between Tasmanian Aborigines and white settlers which eventually resulted in the loss of the purebred aboriginal race from Tasmania. It also typified the misunderstandings that eventually led to more and more aboriginal massacres and attacks from Aborigines.