One of the better ways to avoid taking damage is to hide behind something. This page covers rules for cover and concealment.

Walls, trees, creatures, and other obstacles can provide cover during combat, making a target more difficult to harm. A target can benefit from cover only when an attack or other effect originates on the opposite side of the cover.

There are three degrees of cover. If a target is behind multiple sources of cover, only the most protective degree of cover applies; the degrees aren't added together. For example, if a target is behind a creature that gives cover and a tree trunk that gives improved cover, the target has three-quarters cover.

A target has Cover if an obstacle blocks at least half of its body. The obstacle might be a low wall, a large piece of furniture, a narrow tree trunk, or a creature, whether that creature is an enemy or a friend. When an attack roll is made against a target with Cover, if either of the dice in any attack roll comes up showing a one, the result is a Failure, regardless of the amount rolled. This is often referred to as Cover 1.

A target has Improved Cover if about three-quarters of it is covered by an obstacle. The obstacle might be a portcullis, an arrow slit, or a thick tree trunk. When an attack roll is made against a target with Improved Cover, if either of the dice in any attack roll comes up showing a one, two or three, the result is a Failure, regardless of the amount rolled. This is typically referred to as Cover 3.

A target with Total Cover can't be targeted directly by an attack, although some attacks can reach such a target by including it in an area of effect. A target has Total Cover if it is completely behind an obstacle.

A character's shield can provide Cover if they have Raised their Shield. They gain the shield's Cover, unless Cover from other sources is better.

A creature that is Concealed is out of direct line of sight, but there is nothing tangible between it and any attackers. Concealment works much like cover, though it is not as effective. When an attack roll or a Perception skill check is made against a Concealed target, if either of the dice in any attack roll comes up showing a one or a two, the result is a Failure, regardless of the amount rolled.

A character with Improved Cover or Total Cover is also considered to be Concealed, and therefore, their Cover also affects Perception skill checks.