"Call me naive but I truly believe I am the right guy in the right moment," the Portuguese said when speaking to the media on Friday for the first time since taking over at Old Trafford.
Amorim, who has signed a two-and-a-half-year contract, is United's sixth permanent managerial hire since the great Alex Ferguson retired in 2013.
The 20-time league champions have not won the title since then and have faced more than a decade of onfield decline.
Former Sporting Lisbon coach Amorim follows David Moyes, Louis van Gaal, Jose Mourinho, Ole Gunnar Solskjaer and Erik ten Hag in trying to return the club to the summit of English and European soccer.
"I am a little bit a dreamer and I believe in myself and I believe in the club," Amorim said ahead of his first game in charge against Ipswich on Sunday.
"I don't know how long it will take. I know that when you are in Manchester United you have to win games, so I will not tell you that I need a lot of time.
"Of course we need a lot of time because it is a great league, it's the strongest in the world and we have to improve a lot to try to win. We have to win games to win time and then we have to win titles."
Amorim, who has won two Portuguese league titles, dismissed the idea that managing United has become the impossible job since Ferguson's retirement.
Ferguson is regarded as one of the greatest managers of all time and won 28 major trophies with United, including 13 Premier League titles and two Champions Leagues.
Following in his footsteps proved too much for even serial winners like van Gaal and Mourinho, who had gilded careers at some of Europe's biggest clubs.
Ten Hag took over in 2022 having won three Dutch league titles with Ajax. Despite leading United to two domestic cup titles in his two full seasons at Old Trafford, he was fired last month after overseeing a woeful start to the campaign that left his team 14th in the standings.
"You have different types of coaches, the same results. We will try to do it in our way," Amorim said.
Amorim has a job on his hands just turning United's season around after they made their worst league start since 1986. They're 13th in the standings, but only four points off third-placed Chelsea.
