To be Hidden, you must first successfully use the Hide ability, or an ability that can give the Hidden status effect.

While Sneaking you move at half speed. Any movement while hidden, you must END the movement behind Partial Cover or Full Cover.

This means the character must have some type of obscurement to ALL hostile creatures in the encounter (as creatures will communicate if they see a creature trying to hide).

Once the Caster is Hidden, the Caster CANNOT be directly the Target by hostile creatures, and is considered heavily obscured. But can still be hit by AOE abilities or spells. Hidden creatures can disappear from visibility from the encounter.

Making an Attention skill roll once per turn can have you try to spot hidden creatures. This Contesting Roll is made where you roll against the creature, or potential creature that may be hidden.

If successfully Hidden, Attack Roll the creature does, is considered at Advantage.

The GM may also grant Surprised if this is acted outside of combat/initiative. The GM can do this by rolling players sneak button from the campaign controls.