You place the Fitbit on your wrist, and the Fitbit sends the number of steps you walk to your iPhone. You can use the Fitbit app on your phone as a food diary, too.
I had an ulterior motive for the Fitbit, I thought it would be perfect for my 94 year old Dad, so I got him one as well. Now, we're Fitbit friends, and, since he's so competitive, he's beating me in number of steps taken!
This was pretty easy to set up, but I found the wrist snap difficult to maneuver.