So that's SAS (yaw is usually the first thing that's SAS'd following by pitch and roll but rarely collective). The actuator for SAS is in line with the controls so you cannot feel it working but it definitely moves the same control surfaces (in 99% of cases). They can be either electromechanical or hydraulic -mechanical in nature . They might be called SEMA or series actuators or something like that. Designers of aircraft need to demonstrate that a runaway of these fast acting actuators cannot cause such a significant upset that the pilot cannot safely recover from it.
Generally SAS takes a challenging or spritely aircraft and transforms it into a more predictable but still VFR machine. The sensors in the system usually sense or read the attitude rate of the aircraft so actually have no ideal what attitude you're in. However since it stops unwanted rates building up you get what's called pseudo attitude hold. It feels like it is holding your attitude but that's not strictly true.
Now with this system you can still have some sort of associated trim system. In anything other than small helicopters where you have hydraulic main rotor control, there's no feedback on the controls. So generally a trim system is included to: one, hold the stick where you leave it, two, provide artificial feel (so the pilot has feedback about how far he is moving away controls away from trim). This may then give the pilot the option of temporarily removing the forces (force trim release) and/or beeping the trim position (beeper trim) and/or moving the control to a new position through against friction (typically in yaw or collective). Some aircraft have all three optkons, some less, some different for different axes.
All these various trim options do is change the neutral point. It so happens that the trim system is generally also a core part of the autopilot which is where we go next.