"I'd like to think I've changed, perhaps for the better," he told CNN's Christiane Amanpour. "I've learned a lot about myself, I've grown a lot, I've learned a lot about my family, my incredible family."
Greste, whom Egypt released and deported over the weekend, landed in Brisbane early Thursday morning.
Greste and fellow Al Jazeera journalists Mohamed Fadel Fahmy and Baher Mohamed were arrested in Egypt in December 2013, accused of supporting the banned Muslim Brotherhood. All three were convicted and imprisoned but have maintained their innocence. Greste, who spent about 400 days in prison, had been sentenced to seven years.
Fahmy and Mohamed remain in prison. Greste said at a press conference that he'll work to free them.
"I will do all we can to talk to the right people to facilitate their release," Greste said, declining to go into detail.
Greste thanked the people who worked for his release -- his family, leaders of the Australian and Latvian governments, people who took part in demonstrations and journalists. He was surprised at the number of people involved.
"What we've seen out of this is a sense of purpose and a sense of unity that has blown me away," he said.
Greste said prison was not easy but that he and the others were not mistreated. He was able to work on a master's degree in governmental relations and wrote his papers in pencil and paper.
"We had access to all the things we needed," he said. "The fact is I'm in pretty good health. We weren't abused in any way. We were treated with respect and dignity as much as could be expected under the circumstances"
He fought off negative feelings by meditating. When his thoughts wandered, he imagined going to the beach, something he's already done since returning to Australia.
"To actually stand there and feel (the sand) between your toes was awesome," he said.
Greste said he and his colleagues talked about the possibility that one of them would be released before the others.
"They were all very happy for me," he said. "You can imagine after 400 days of imprisonment with these guys we were very close."
When they are released, Greste said, "I will party with them very hardy indeed."
Arriving at the airport Thursday, Greste, wearing a checkered shirt and jeans, was cheered by a crowd of dozens who had awaited his arrival. He smiled, hugged several people in the crowd and flashed peace signs with two raised hands.
Greste said he's not sure what will happen in his immediate future but expects to return to journalism.
"I don't want to give this up," he said. "I'm a correspondent. It's what I do."
When his mother, Lois Greste, was asked how she felt about that, she said, "We've always believed our children should follow their passions and Peter's doing that. At the same time, he's got to know we aren't going to go through this again."