How can assemble the core with servo motor!

One other thing to watch out for is that only certain pins support servos--A0 should be fine.

attach()

Set up a servo on a particular pin. Note that, on the Spark Core, Servo can only be attached to pins with a timer (A0, A1, A4, A5, A6, A7, D0, and D1).

@Bdub did a great servo demo with Facebook likes over here: