Can any body tell me the concept of ESC?? I have the following questions:

- whats the relationship between the ESC compatibility and the motor's number of turns?
- What make an ESC good? Bad?
- How come some ESC can reverse and some can't?
- I've noticed a little button on my ESC (Don't know the name), and whenever something's not right, my friend just clicked on it for many times until he gets it working. He never told me when I asked him about it. What is that button and whats its purpose?

Thank you. Any comment will be greatly appreciated.