An object will accelerate in the direction of the what?
An object will accelerate in the direction of the net force acting on that object.
Is Centripetal force causes an object to accelerate in a fixed direction true about centripetal force?
This can often be slightly confusing and this is a simplistic explaination. An object is said to accelerate when either the velocity, direction or both changes. As an object in orbit is constantly changing direction if not speed then it is said to be accelerating. Sometimes confused with a vector which has the properties of both direction and speed.
This depends on in which direction the force is being applied. If the force is applied against the direction of movement, it will slow a body down If the force is applied in the same direction of movement then it will cause the body to accelerate. If the force is applied in a direction at angle to the motion, the force can either cause the object to slow down or accelerate depending on the angle.