Upon entering any brush, the unit is immediately rendered invisible to enemies outside of that particular patch of brush, a state that is represented when the unit's model takes on a partially transparent quality. The unit will remain invisible as such until it has either left the brush, is revealed by a sight-granting ability, item or an enemy unit, or engages in most kinds of attacks.
The unique properties of brush and its ability to manipulate the sight of an opponent affords several key tactical advantages. Most notably, any kind of unit-targeted ability cannot be used on an opponent hidden within brush whatsoever, meaning deliberately entering one to break lines of sight can force enemy champions who rely predominantly on this casting type (such as Fiddlesticks) to waste resources or time on reacquiring sight of their target. It is also a key factor in almost any kind of ambush, or ganks, allowing an aggressor to remain hidden until their target is close by or out of safety. A technique known as juking is commonly employed using brush to invoke unpredictable changes in direction when fleeing, and the same unpredictability can also allow for disguising a vulnerable channel time, such as Nunu's Absolute Zero.
Brush does not provide not true stealth, as the unit does not require any form of true sight in order to be visible, but the widespread distribution of brush around the various maps nonetheless mean that using brush correctly is a nigh-universal skill to learn in high levels of League of Legends play.
All forms of autoattack and the majority of non-skillshot offensive abilities will reveal the caster and a small area around them for a short period of time, if they are standing in brush. It is therefore generally impossible to remain permanently stealthed while attacking, although the element of surprise granted by brush can still be significant.
While the most direct way of scouting a suspicious brush involves the user personally entering to inspect it (more commonly known as facechecking) almost all abilities, spells and items that provide sight can be used to reveal the interior of a brush. Most prominently, wards are a very common answer to tactical attempts to utilize brush. Wards are subject to the same limitations surrounding brush as other units; they will reveal the area inside the brush, as well as the area surrounding it, and a placed outside of a brush will not be able to see enemies inside. Because of these reasons, it is extremely common to place a ward within a brush and effectively negate its use by the opposing team for as long as the ward lasts.
If the champion is capable of summoning pets or possesses one that is controllable, they can also be ordered into the brush to scout.
Aside from gaining sight, brushes can also be scouted indirectly using certain abilities that play a sound effect or otherwise behave differently when striking a champion inside brush, such as Infected Cleaver making a noticeable 'splat' sound and refunding health to Dr Mundo whenever it impacts an enemy champion. Most collision skillshots (such as Ashe's Volley) will visibly stop short within the brush if they collide with a unit, even if there is no noticeable effect otherwise. Auto-targeted abilities that cannot be used unless an enemy champion is in range can also indicate if a brush is occupied provided the user is close enough.