... how do they work, when triped are they somehow self resetting ? Also are they good for many trips ?
Yes, they reset themselves. Typically, unless seriously overloaded (e.g.: direct short circuit) They reset as often as needed.
There is a metal strip that when overheated, pop open a set of contacts, once cooled down, pops back into place. Bi-metal strip I believe, works a lot like a turn signal flasher does.