What two characteristics differentiate a robot from a machine?

A robot is a virtual or mechanical artificial agent. In practice, it is usually an car engine electro-mechanical system which, by its appearance or movements, conveys a sense that it has intent or agency of its own.

A machine is any mechanical or electrical device that transmits or modifies energy to perform or assist in the performance of human tasks.

A machine is, for example, a car; pieces put together in the right way to make it go after the engine is turned on, with commands given such as acceleration, braking, turning, drive, park, neutral, and so forth.

A robot is programmed to do a specific task, and accomplishes this when its "master" turns it on. It can accomplish its tasks, assuming it is fully capable, without any more assistance by outside beings.