Brown joins the Hammers after spending his schoolboy career with Arsenal.
"I'm a No9 and my objective in a game is to score goals," Brown told whufc.com. "I want to help the team out and to lead from the front. I'm quick and strong and I think I can run with the ball as well. I'm an attacker.
"I'd been at Arsenal at eight years and they wanted to keep me, but I sat down with my parents and my agents and we thought it was a better decision to come to West Ham. The opportunities are here and I thought, at Arsenal, maybe I could have faded away because I've seen it happen before.
"I thought, the opportunity was there for me at West Ham and it has the attributes for me to be what I want to be in football."