Rooney has signed with the DC-based club for three and a half seasons.
"I want to win, that's the way I have always been and while I am playing football that will remain the same," Rooney said to Sky Sports.
"I have not come here to wind down or to just come and enjoy the place. I have come here to play and win.
"It is a massive decision but we felt it was the right one. It was the right time and there are no regrets."