How stealth works in combat?

Maybe I miss something in this gigantic 600 pages of a book. But how stealth works in combat? The only info I have is that you cannot run while stealth in combat. There is also a surprise conditions but from what I read it is for before the combat start not during. There is a talent that let you do Run action in combat while stealth but how stealth works in combat to begin with? What is the benefit? Thanks guys