You are skilled at avoiding detection, allowing you to slip past foes, hide, or conceal an item.
First, Hide behind something (either by taking advantage of cover or having the concealed condition due to fog, a spell, or a similar effect). A successful Stealth check makes you hidden, though the creatures still know roughly where you are.
Second, now that you’re hidden, you can Sneak. That means you can move at half your Speed and attempt another Stealth check. If it’s successful, you’re now undetected. That means the creatures don’t know which square you’re in anymore.
If you were approaching creatures that didn’t know you were there, you could begin Sneaking right away, since they didn’t know your location to start with. Some actions can cause you to become observed again, but they’re mostly what you’d expect: standing out in the open, attacking someone, making a bunch of noise, and so forth. If you Strike someone after successfully Hiding or Sneaking, though, they’re flat-footed to that Strike.
Creatures can try to find you using the Seek action.
Three conditions explain the states of detection.
Remember that these conditions are relative to each creature—you can be observed by one creature while hidden to another and undetected by a third.
You’re in the creature’s clear view.
The creature knows your location but can’t see you.
The creature doesn’t know your location.