system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do mind-controlled prosthetics actually work? And how do they "feel" when worn?
gpt
Mind controlled prosthetics work the same way your current limbs work - actuators respond to signals sent by the brain.

Normally, your actuators are your muscles and tendons. Starting out, you have very, very poor motor control(babies), and as your grow your brain gets better at sending signals to your muscles and tendons to do increasingly complex tasks.

Now replace muscles and tendons with servo-motors. Your brain is still sending out signals to the now missing limb; through a combination of electronics interpreting those signals and the brain re-training itself on what signals to send to achieve a given motion you gain the ability to move a prosthetic. The electronics may be taking measurements from muscle groups further up the affected limb, they may be reading brain waves, hell they may be taking readings from an implant in your brain. 

The better the electronics interpreting the existing signals are, the better you will be initially at using your replacement finger/hand/arm/foot/leg, but like everything you have ever learned to do practice is needed to improve function - just like babies learning to use their hands etc.

as for how they feel when work - most of them don't offer any kind of feedback loop - if you aren't using some sense other than touch to realize your hand is squeezing a bottle too tightly, you don't know how tightly you are gripping. Some prosthetics do attempt to provide some kind of haptic feedback where prosthetic meets flesh to indicate resistance in a particular joint etc.

There have been some interesting clinical results though, where people have had direct brain implants and have reported being able to feel through their new limb.