Help connecting an Arduino and an electronic speed controller
HobbyKing, which sells Arduinos and is a great source for motors and controllers, has an instructable on this at http://www.instructables.com/id/ESC-Programming-on-Arduino-Hobbyking-ESC/

I found another on the OpenROV site, at http://community.openrov.com/forum/topics/how-do-i-activate-electric-speed-controller-with-arduino

Did you actually try googling "arduino electronic speed control" before coming here?