The Scot, appointed as the successor to Slaven Bilic at London Stadium, takes over with West Ham in the Premier League relegation zone.
Moyes has been out of work since leaving Sunderland in the wake of last season's relegation to the Championship, while he was sacked by Real Sociedad and Manchester United after lasting less than a year at each club.
The 54-year-old said it was a simple decision to take over at West Ham - despite only being given a contract to the end of the season - and accepted he will need to rebuild his reputation.
"I was in Qatar doing some TV work and was asked if there was interest, (I) said yes very quickly," Moyes told a news conference on Thursday (AEDT). "Couple of quick meetings and I find myself here now.
"It's good for me. I am back in, it's what I love doing, it's what I do. I want to do well, I want the team to do well. I also think it's good for West Ham, I think I am a good manager."
Of the length of his initial deal, he said: "I am more than comfortable and so are they. Managers now aren't having long-term contracts and we'll see managers sign one-year contracts in the future.
"If I had taken over at the start of the season, I would have said let's take it a year at a time. It gives me a chance to look at the club and gives the supporters a chance to see David Moyes working.
"This was a really easy decision to make. West Ham is a top club, great stadium and we will grow into it," he said of the club's new home, which they have struggled to adapt to since leaving the Boleyn Ground in 2016.
"I hope that the future is great for West Ham. My ambition is only short term because I have to win the games. I want to win the games, get away from the wrong end of the table, the squad is good enough.
"I have a point to prove. Sometimes you have to repair things and maybe I have a little bit that I need to repair."
Moyes takes over a team that has conceded 11 goals in their last four games in all competitions, although they are in the quarter-finals of the EFL Cup, where they will face Arsenal.
And the Scot will prioritise defensive stability within the team, who are 18th in the table, a point away from safety, ahead of his Hammers bow at Watford on November 20.
"I love to see goals and attacking play, I want us to be entertaining," Moyes said. "But it's no good if you're shipping goals. All the best teams have the best defences so we have to start with that.
"We have to get ourselves clean sheets, get bedded down. Let's see if we can find a way of stopping conceding goals.
"I want to bring winning football first off before we talk about style. There's a really strong squad of players here. They certainly shouldn't be in the position they are in.
"First of all, let's get winning. I'll do everything I can to get West Ham as far up the table as I can. The players have to take responsibility too and show they are good enough to play for the club. They have to show that.
"My biggest challenge is I know I have a game coming up and I have to get the team ready and the games come thick and fast.
"I am well aware we have a lot of tough games coming up. I want to get us ready to put on a good show in those games.
"I wanted a big challenge. West Ham is a top club and I want to be a success."