CJ, sensors (gyro, accelerometers etc), AFCS computers, linear and parallel actuators - all electronic. The flying controls - rods, levers, wires etc to hydraulic servo jacks.
The AFCS computers can either input directly to the servo jacks (usually SAS) or use open loop actuators directly onto the flying control runs.
That is a simplistic and generic overview and not aircraft specific as there are many variations.
The main problem with modern AFCS is that they are made complex by engineers and need to be treated like any other computer - ie garbage in equals garbage out.
If you tell it to do the wrong thing, either through an error, ignorance or lack of practice - it will do what you have asked it to - even if that isn't what you wanted or expected.