Vinicius Junior has said he is ready to fight for a place in the Real Madrid first team and will work hard to adapt as quickly as possible.
Vinicius joined up with Madrid for preseason training, with FIFA rules meaning he had to wait until he was 18 before a €45 million transfer, agreed last summer with Flamengo, could go through.
Madrid were reported to be considering loaning him out next season, but he said he expected to remain at the club.
"I am staying at Real Madrid with the first team," he said. "I will play some games with Castilla [the youth team] to adapt as quickly as possible.
"I can do everything I did at Flamengo, and do better. I will show I am ready to play and show everything possible as quickly as I can. I know the adaptation will not be easy, but I am ready to do whatever is necessary.
"I am coming from Flamengo, another club with a lot of pressure. The people around me are here to help me with this. I never think of failing, just succeeding, winning as much as possible."
Vinicius has spent the week training under new Madrid coach Julen Lopetegui ahead of the International Champions Cup in the United States.
"Football is a bit different here, but coach Lopetegui is helping me a lot, telling me what I must do, how I can improve," he said. "This is the best opportunity a football player can have.
"I will sacrifice a lot to show I deserve this opportunity. But sacrifice is not something new for me. I come from a very simple family, and am very proud of all they did for me and the values they have taught me."
Asked whether it was a shame to have missed out on being a teammate of Cristiano Ronaldo, who left Madrid for Juventus, he said: "Cristiano Ronaldo is a legend of Real Madrid.
"But I am very happy to be alongside [Karim] Benzema, [Gareth] Bale, the players I will play with in the future. The best players in the world are here."
Compatriot Neymar has said he will stay at Paris Saint-Germain despite speculation that he could move to the Bernabeu, and Vinicius said he was "my idol."
"I dream of playing with Neymar, and if God wills it, I will play with him soon for Brazil," he said.
Madrid legend Ronaldo Nazario, meanwhile, told his countryman he was at the best place to make progress in his career.
"Here is where I was most happy playing football and won many things," he said. "Maybe it will be difficult at the start, but this the best place you can be."
Madrid president Florentino Perez praised the new addition to his club's ranks, saying: "We said the other day that we would add magnificent players to our squad, and that is what we are doing with Alvaro Odriozola and now with Vinicius.
"Vinicius is one of the great hopes of Brazilian football and world football, but who is already a reality and was wanted by Europe's biggest clubs."