Normally, a character can be seen by anyone in the vicinity. A character can attempt to hide, so that others around him/her are unlikely to see him/her. A hiding character is not invisible; it is simply that a motionless person in cover or shadows is hard to see.
To do this, the character makes a dice roll using his/her Stealth (including hiding specialism) + WP. There is a modifier to the dice roll based on the degree of cover and lighting, from +5 for dense undergrowth and poor light, to -5 for very little cover and bright light. A character's clothing also affects the dice roll; bright garish clothes give a penalty of -2 on a hiding dice roll; on the other hand, if a character is successfully camouflaged, he/she receives a positive modifier to the dice roll.
To spot someone hiding, a character must make a dice roll using his/her Tactics (including Spot hidden specialism)+ PE, and get a dice roll result that is greater than or equal to that achieved by the hiding character. There is a penalty on the hearing dice roll for extensive distractions of between -1 and -6 depending on the extent of distractions (e.g. trying to spot a hiding character on a battlefield). The spotting character gets a +3 bonus on the spotting dice roll if he/she knows the hiding character is in the immediate vicinity (e.g. through having seen the hiding character immediately before they hid).
A hiding character may not move without losing the benefit of hiding (being motionless is one of the key aspects of hiding). However, while the onlookers are not looking, the hider may move quietly from one hiding place to another (e.g. to sneak up on an onlooker). If the onlooker turns around, the hider will need to make a new hiding dice roll to avoid being seen (and may be caught in the open with poor cover if the onlooker turns at the wrong moment).