rotate transform toward a desired direction

hello friends. I wish to rotate my gameobject from the current direction by an angle. i calculated the angle, but struck with rotating the object. please help

var moveDirection : Vector3 = target - transform.position;
var fwd = transform.forward;
var vect : Vector3 = moveDirection.normalized;
var rotationangle = Vector3.Angle(fwd,vect);

the rotation required should be smooth.

Also you should use Unity - Scripting API: Vector3.Slerp for interpolation