Can someone explain the "luck" stat

I'm not a total noob (multiple ds1 play throughs and completed ds3 once, didn't like 2), but there is a whole level of Dark Souls that I just don't understand, basically if dark souls skills were a ladder, I'm one rung above casul. I don't have friends who play, so I don't have a mentor.

Regardless , can someone explain "luck", since it's a new stat. The game says it helps item discovery , but it sounds like there is more to it. Pros and cons?

Thanks in advance.