The 18-year-old midfielder was unveiled by Sir Alex Ferguson at a press conference on Thursday alongside fellow new signing Shinji Kagawa.
And Powell admitted that he did not get much sleep ahead of his first day of training following his move from Crewe Alexandra, but praised his new team-mates for alleviating his nerves and making him feel welcome.
"I didn't really sleep to be honest! I was quite nervous – it felt like I was starting a new school again," he told the club's official website.
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"It's been great. The lads are really nice and they've all helped me through the first week. I feel like I've fitted in well with everyone. The training is different but it's something I'm enjoying and just getting used to.
"I tried to get involved with everyone straight away when I arrived and that helped. And as I said before everyone around the place has been really friendly and welcoming."
Powell added that sharing a dressing-room with Ryan Giggs and Paul Scholes initially left him awestruck, but now he cannot wait to learn from the veteran duo on the training field and hopes to become part of the club's illustrious trophy-winning heritage.
The youngster continued: "Walking into the dressing-room and seeing my name on my peg was a great feeling and the first people I saw were Giggsy and Scholesy. I'm just used to seeing them on TV so it was pretty amazing to see them stood there.
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"They came over straight away and welcomed me, which was great. I'm really looking forward to playing and training with them - Scholesy is a midfield maestro and one of the best in the world ever and then you've got Giggsy who has been running the left wing for over 20 years.
"It's the fact I've joined not only the best team in England, but one of the best in the world. They've won every trophy going on numerous occasions and that's something I want to be part of."