Stealth is the art of not being noticed and escaping detection via sight, sound or on occasion scent.
There are two main uses of the Stealth skill:
In order to use Sneak, a creature must have some means of concealment; an object their size or larger to hide behind or in, dense vegetation, areas of low light or total darkness, etc.
As a Move action, a creature may make a Stealth roll. This roll becomes the DC for a Perception check necessary to detect that creature’s presence. Creatures whose Passive Perception is greater than the DC are automatically aware of the creature using Stealth. Creatures who are unaware of the stealthed creature’s presence are grant it combat advantage.
Creatures actively observing the user of this skill when they make the Stealth roll automatically succeed on their Perception check to remain aware of the stealthed creature.
Leaving one’s means of concealment, running, charging or making a loud noise immediately ends the effects of making the Stealth check for all creatures that could potentially see or hear the stealthed creature.
Making a melee attack against a creature instantly end the effects of making a Stealth check against that creature. A stealthed creature making a ranged attack against another creature must make an opposed Stealth check against the target’s Perception check; if the attack was made with a Firearm, the Perception check gains a +5 circumstance bonus.
Moving at more than half speed while stealthed allows all creatures that could potentially see or hear the stealthed creature to rereoll their Perception checks with a +5 to the roll.
Hiding is the act of concealing oneself behind, inside or under objects like boulders, closets and haystacks respectively.
While in a hiding place, a Hide check becomes the DC for the Insight check used to discern your hiding place. Certain hiding places or objects grant a circumstance bonus to the Hide check.