Stealth Dice have two main uses:

LOWERING DANGER

While Exploring (NOT while in Battle), Characters may Roll Stealth to lower the current Danger Level.
As with Rolling any Character Dice, the act of the Rolling will also reset the dice into new forms.

INSTANT TURNS

While in Battle (NOT while Exploring), Characters may Roll Stealth to Attack a Monster out-of-turn.

• When first encountering a Monster, this can be attempted to Attack the Monster first (before it Attacks)

• After Attacking a Monster, this can be attempted to try to Attack immediately again
  

Instant Turns are NOT guaranteed. When the Stealth is rolled, the result(s) must equal or beat the current Dungeon Level.
(as long as one of the results is high enough, the Instant Turn is a success)

RISK:

If an Instant Turn succeeds BUT the Group does not/cannot Attack again immediately, the Monster immediately get X Attacks in a row (= current Dungeon Level)

As with Rolling any Character Dice, the act of the Rolling will also reset the dice into new forms.