The Scot, who replaced sacked Slaven Bilic on Tuesday, said he will do all he can to ensure "winning football" at the London Stadium.
"I've been a football supporter all my days and I love to see attacking play and goals," he told a news conference on Wednesday. "But that's no good if you're shipping in goals every week because you can't win the games. You have to start defensively.
"We have to start from there, try and get a few clean sheets, find out whether three or four at the back is best for us with the players available, and get ourselves bedded down.
"I think we have enough good attacking players to cause teams problems and score goals. Let’s see if we can find a way to stop conceding goals."
Moyes, who started his managerial career at Preston North End, forged his reputation at Everton from 2002 to 2013, an 11-year spell during which he guided them to a top-eight finish nine times.
The 54-year-old's stock has fallen considerably in recent years, following an unsuccessful period at Spanish side Real Sociedad after a short-lived time as Alex Ferguson's successor at Manchester United in 2013-14.
Moyes has been out of work since May, when he resigned as Sunderland boss after the club's relegation to the second division.
"It is good for West Ham, they are getting a good manager," he added.
"I do have a point to prove. Sometimes you have to repair things and I have a little bit to repair. I want to get back and want to do well."
Moyes's first assignment at West Ham will be a league trip to ninth-placed Watford on Nov. 19.
(Reporting by Hardik Vyas in Bengaluru; Editing by Toby Davis)
